You say “boyfriend,” so that means you’re not married. If you aren’t married, then I fail to see how she’s your “stepdaughter.” She is your boyfriend’s daughter. 

All this to say, she is not your problem, though I do see problems within this living arrangement. Do you and your boyfriend equally contribute to the household (rent/house payment/utilities, etc...)? 

Also, she’s 18. Is she in school? Work? Regardless, she needs to be contributing to the household, somehow, someway. Especially so if she doesn’t work. Would your boyfriend just live in squalor if you weren’t there to clean? What did he do before you came along? 

Pull back on what you do for his kids. Focus on you, your relationship, work, or like you said - moving out. 

If your SD is 18 she is an adult, and irrespective of that, should be expected to be civil to other members of the household, and also pull her weight with some chores, regardless of her school and job responsibilities, IMO.  

Does your BF contribute to the household chores?  He should be doing, if you both work.  If you make yourself into a doormat, sadly, people will walk on you. 

It literally takes two minutes to unload a dishwasher, I've timed it.

DH used to give the same excuse.  The problem here is not the time or work, it's the indignity of cleaning up after a child like the hired help.  I would thoroughly clean the house only to find ramen sprinkled all over the kitchen like confetti an hour later.  Left for me to clean up.

So I went on strike.  I no longer cook or clean.  I eat at work, and use the master bathroom only when home.  On the rare occassion I eat something at home, I unload the dishwasher and put my one dish in.  I vacuum and dust and clean a toilet every once in a long while, commensurate with my use.

DH gets to clean up after his feral pig.

Is your bf physically disabled that he can't wash the dishes? 

Well, I guess you have too much on your plate with working overnights to cook and clean for his kids. Too bad.  I guess they will have to go somewhere else when he's not home. 

He thinks because I'm the adult that I should make the extra effort to talk to her.

^^^^^^^^^^ He has an 18 year old daughter that he continues to make excuses for. Since he won't follow through on what needs to be done in the home I'd disengage and possibly reconsider living with him and this arrangement. None of it benefits you and its not worth the frustration if your BF doesn't see anything wrong with it. This will continue to be your life until you take control of it.

Leave. You have an autistic 'step son', a rude feral 'step daughter', and a lazy boyfriend that provides nothing but excuses. You pay the bills, cook, and clean and cannot relax in your own home...why do you put up with this? You're not married, this really is the best it's going to get. There is a good chance that one or both kids will live with Daddy indefinitely. You are being used. You would be better off by yourself.

Yea, he definitely sucks.

When are you moving out?

ditto

Time to turn her bedroom into the land fill of the house. Anything not picked, dump in her room.  Lather, rinse, repeat.

If that doesn't work...start taking it to the curb. She can deal with it or it goes to the dump with the rest of the garbage.

An 18yo can contribute to keeping the home clean... so can your BF for that matter.  Time to get out of the live in sugar mama beck and call girl/chore bitch business and let these nasty people simmer in the their own rot.

Move on. Take your money with you.

smh.