Honestly? If he won't stand up to his family to not raise a total brat and if he won't stand up for you then leave.

Your daughter is essentially being torured at school by this brat, he is not stopping it, he won't stop his family from treating you poorly, its like pulling teeth to get him to do anything. Why are you with him?

Well, your BF has been a father to her for 14 years, sees no problem with his parenting, and along comes YOU and YOU are trying to change the whole dynamic between them.

Girl, you are setting yourself up for nothing but headaches and heartaches.

My suggestion? Shut up. Let him parent the way he wants to parent. Don't move in with him or marry him until she's grown. Your actions are doing NOTHING but making your life miserable. Can you not see that? The absolute worst part of this is that your actions are now affecting your daughter, and in the ugly world of high school. According to GM, you're brainwashing daddy. While I disagree that it's "brainwashing," she has a point.
YOU ARE TRYING TO CHANGE YOUR BF INTO SOMETHING YOU THINK HE SHOULD BE.

For the record, I disagree with his parenting. I don't and haven't parented my children the way he does. However, you need to recognize, for your sanity, that this is not your battle to fight. Keep your lives separate until she's grown, and enjoy going on dates with him.

I get the adoration and not wanting to leave, but, unless your BF stands up for you to SD and tells her to STFU (in a much nicer way, of course) when she tells him to choose between the two of you, then, you might not have any other options.

She's manipulating him and trying to force his hand by telling him he needs to choose and that if he chooses "wrong" she'll leave. And that's F*CKED UP. She thinks it's a game and that it's an either or contest when it so isn't. You're his significant other, she's his DAUGHTER, there's no comparison to be made, but, these twisted SDs make that comparison because someone, somewhere along the line led them to believe that they were the "wife".

And if your BF doesn't tell her as much, then, I'm not sure what else you can do besides leave. That's a big reason why I'm still with my SO, because he finally stood up for me to my SD12 and told her that this isn't a contest or a game and that she's acting inappropriately by trying to make him choose between both of us. Once upon a time, SO had said that he didn't know if a relationship between us could work if SD didn't like me. I had agreed because, at the time, I was sipping the kool aid and didn't think it would be possible myself. But, three years later, he realized the errors of his ways and how it was unfair to put any of us in that kind of a situation because I encompass a completely different role in his life than SD does. He told her all that and told me that he would not let his kid's rotten attitude ruin our relationship. If he hadn't done that, well, then, I would have left.

If there's really a lot of money here, perhaps both girls could go to different boarding schools, first one and then the other. I'm guessing you live in France from the description of the educational system, so there are private schools around. If you are American, there may be an American school; if the SD is not, then some school for French (or whatever) girls.

It's difficult blending families where kids knew each other from school. A boy went to school (probably 50 years ago) with a friend of mine. He was thinking he sort of liked her (unknown to her for 50 years), then, his father married her mother to everyone's surprise. Parents spent a lot of time drinking, he was confused, he persecuted her at school because he just didn't know what to do with his feelings. He and his feelings hurt her dreadfully at the time, and her mother witnessed this with no support or even insight. Fifty years later he tells her be actually liked her and was sorry if he hurt her -- ended up that his son went to the same college as her daughter and the kids and then the adults met. No fireworks there as both were married to others, but it took my friend years after her mother and his father divorced to recapture her self-esteem. Her mother eventually went on to have at least three husbands (in the middle marriage to the boy's father, Mom emulated the atheism of her husband and ridiculted her children's Christian faith, then back to Christianity with her final husband). Her father married four times.

Sometimes I go on like this about how former stepchildren see all their parents and steps because so many people on this site present themselves as the soul of reason dealing with sociopaths. Just remember next time you're despsiing some quality of the stepchild (also known as stepshit here by people who complain that the stepshit does not respect them) that the child's relationship to your spouse may survive your marriage to him/her and that reasonable minds may differ about what's going on with you and the marriage. That is, if you're drinking and ridiculing your children's faith, it may be that you'll have a change of opinion about God or booze. The children (yours or your spouse's) are observing you and drawing conclusions. Given that your opinion may be happiness or despair for the kids, they can be acute observers.

Another thing to consider: the entitled brat who demands material things may be acting under orders, the biological mother's or even her new husband's. With no place to go but YOUR house if they do not comply, they hardly are in a place to disobey.