Your entire post is a giant red flag.

I think you're too far in, too quick.
This little girl runs the house because mom is letting her. If she wont put her foot down, see how she reacts if you put yours down. You dont want SD sleeping in the bed with you. {I completely understand this, I didn't want SS sleeping in our bed either because it was weird to have a child not related to me in bed with me. But I also dont want our BD to sleep in our bed now. Tho my husband constantly will put her in your bed at night. My solution was a little mat at the foot of our bed. We told SS and our D figured out that if they wake up and are scared or whatever, they can come into our room and lay on the sleeping bag mat. I suggest implementing that option for your sanity as well. And explain to FSD, you need to sleep in your room like big girls you've age, and if you do wake up in the middle of the night or early morning- you can come lay on this lil blanket here in our room. You can't climb into our bed anymore because they're isnt enough room for 2 adults and a big girl like you.
I do think your SO is more interested in what her ex says than what you say- so that in of itself is a red flag. Co-parenting, where everybody can get along like one big happy family only works if the parents are friendly-which clearly they are not. They need a strict CO and to follow that exactly, no if ands or buts- or both parties will be angry all the time. For SD, she needs to set up rules for her house because SDs dad is not there to do it anymore. If she doesn't know what to do, offer suggestions, there's also parenting classes; basically support her. And full custody doesnt mean completely losing out, since the situation is split 50-50, they'll likely try to keep it about the same unless there's some reason why Dad shouldn't get SD more (if so, then you'll only be SD free EOW-every other weekend). So it'll be either school and vacation parent or longer splits, switching monthly instead of weekly (which is probably in the best interest of the child at 5- every other week gets confusing).

Also discuss all this with your fiance. What does she expect you to do in the house? Just be a money spot or an equal partner? If its the later, then you'll have to agree on everything exclusively between you two and if its the first, then run out now.
Good luck.

This situation really does sound ugly...EVERYthing about it.

The relationship between your gf & her ex doesn't sound like it's finished. There is too much bantering & emotional interaction.

The child is 5, which means you have at least 13 more years to endure this, & that's if your gf is willing to cut the strings when her daughter becomes an adult. There's no guarantee that will happen.

There is a serious need for boundaries, both between your gf & her daughter (the rules regarding the adult bed) & between your gf & her ex in order for things to improve.

As for the little girl...she's 5. Children that young typically aren't respectful of other people's things. They throw tantrums, & they want to be entertained. She wants to be in the big bed with the grown-ups. That's typical 5-year old behavior. HOWEVER, she needs to be taught to behave properly & respect people's space, time, & things. She needs to be taught to entertain herself sometimes. That will only happen if your gf is willing to teach her & create those boundaries.

The petty bickering about her not being willing to switch weekends out of spite...it's stupid & that attitude is going to create more waves than peace in the situation. She needs to get over herself & not let her bitterness make issues that wouldn't otherwise be there. Steplife is difficult, even when everyone is on the same page. The adults need to behave like adults.

If there are issues between her & the ex that have been pushed into corners & swept under rugs, they need to deal with those & hash them out before moving forward. No need to drag that crap into new relationships.

First off let me say welcome! I joined this site about a year and a half ago and it has helped me deal with my situation immensely! I am 27, and my husband is 31. We met when I was 21 and his daughter was not quite 2 1/2 years old. He was still married but he had filed for divorce about 3 months before we met. Unfortunately I had to wait about a year for it to be finalized!! His daughter had slept in the bed with him up until that point. When we moved in together just 4 short months later, that definitely came to a halt. Granted we moved into a new place and she now had her own bedroom. She would wake up in the night and my DH would just walk her back to her room and lay on her floor until she fell asleep. I hated weekend mornings in the beginning because she would just come in and jump in his side of the bed and he would let her stay there until he got up. I like to sleep naked so I was highly uncomfortable to say the least!! I would have to wait until they left the room before I could even get out of the bed. That went on for a while until she just grew out of it maybe around 3 1/2-4 years old. Then she just began to come into our room and stand there pulling on Daddy's arm until he got up to feed her breakfast. Now at 8 years old my SD doesn't even set foot in our bedroom really. Last year my husband told her she is not to enter our bedroom freely, it is our private place, and not a play room. I also can understand the annoyance of a loud and rude child in public...it is embarrassing and I feel that it is a product of a spoiled child. Children that act that way are obviously not reprimanded for their actions because if they knew there was a consequence chances are they wouldn't act that way in the first place. My SD will occasionally pull that crap in public but she knows better because her Dad doesn't put up with it. I am lucky in that my husband always disciplines his daughter and doesn't let her get away with acting like a brat. But she definitely does spout off with it on occasion and I honestly think it is because her Mom and her Grandma let her get away with murder. She runs rampant at her Mothers house and is never punished when she is bad. Her grandma (My Mother in law) allowes my SD to back talk and just talk to her like crap and she never disciplines her. And regarding the child that always cries bored...my SD still to this day would like us to entertain her 24/7 if we were willing. She has a room full of toys, a television with a dvd player, but she would always rather play a game with her Dad and I or she wants to play video games or watch tv on our big screen in the living room. It is frustrating! I don't know why these children are so needy. I remember playing by myself all the time when I was little! My parents were not my constant play things. UGH! To put it simply it is just not an easy job being a step parent. In fact it is one of the hardest jobs I have ever had. There are resentments that pop up, jealousy, and anger at times. And when the ex of your spouse is uncooperative it makes it that much worse. The birth mother that I have to deal with is a nightmare and nothing is ever easy. I noticed you said you had to give up your schooling. You are already making sacrifices at the young age of 23 for your partner who likely had her time to be there and do that. Is that something you will grow to resent? I know for me, I struggled a lot with the things I gave up to live with my husband and his child. I was just 21 with the whole world at my finger tips!! It was hard to give up partying with my girlfriends and coming and going whenever I pleased without ever having to consider anyone elses feelings or wishes. This site helped me because I am able to vent and say things that might be hurtful if I were to say them out loud to my husband. It is nice to know there are other step parents out there that can relate and won't (usually) judge you. If you love your partner enough..you will find a way to make it work. My husband and I broke up 4 times within our first 2 years together but we made it through those tough times and that makes me believe we are meant to be together. It took compromise and effort on both ends. You need to meet in the middle. I am glad we waited until our 5 year anniversary to get engaged because we were able to work through a wholllle lot of issues before we tied the knot. I would suggest you tell your girlfriend exactly how you feel about the situation! If you pretend all is well you will eventually blow up one day from holding it all in. You are definitely not alone and I hope you find some relief here. GOOD LUCK!!!!!

You shouldn't stuff your dreams in a sack for ANYONE!!! You will regret & resent. You are only 23....live your life. Find someone without baggage that you can start a life with and have all of your firsts together. If you are only 6 months in, get out now while you still can! Take it from someone who wishes they would have done things differently.

I'm so confused!!! It sounds like you are living together? After 6 months? WHAT!? She is no longer the person you fell in love with?? After 6 MONTHS?! And you think you have invested too much time? You are in the honeymoon phase, if you are out of love, get OUT.

Listen to hippiegirl. You are too young to be worried about this crap. There are plenty of great single girls your age out there without kids, or even single moms who don't have ex issues and have wonderful kids. Marriage is forever, and you can't even take 6 months. RUN