Posting from a dummy account for obvious reasons.

Husband and I have full custody of his son Luke 15M. Luke is an amazing boy and I truly consider him my son. The problem is that I was told sometimes I am too overprotective of him and that's why I am doubting myself with this situation.

Husband's sister Anna has a daughter Cassie 14F (so Luke's cousin). They used to be close while growing up but ever since they reached puberty they grew apart mostly due to different interests. Luke is into everything related to computers and his dream is to become a game developer. We signed him up to extra classes for programming and he is very invested in this. He made a couple of friends there who share the same passion like him and they are now working on creating their first mobile game. The boys are good kids and we often host them at our place for them to work on their project and have fun.

Cassie does not really have friends and she wants to spend a lot of time with Luke. The problem is that Cassie came out as a lesbian and she's bringing this up constantly. We don't judge her for this but she is a little too much making everything about her sexuality which in turn makes people uncomfortable. Some examples: during family celebrations she suddenly starts saying out loud how happy she is now that she came out and can openly admit she is a lesbian. The first time you hear it, you tell her good for you etc. But then when we hear it over and over again every time we see her, what are we supposed to say? She will also loudly declare to everybody each time she has a crush, when she had her first kiss with another girl or what body parts she appreciates in a girl. One time my MIL was telling us that one of my husband's cousin got breast implants and how her chest is huge. Cassie told MIL that she is very attracted to girls with big chest...So this kind of akward situations.

Luke came to husband and I and told us he does not want Cassie at our house anymore. He told us she is making him uncomfortable by insisting on talking about girls with him and when he does not engage, she will tell him he must be gay. He told us what she does is her problem, but he has other hobbies and passions and does not want to discuss with his cousin what a nice ass some girl may have. Apparently this is everything Cassie wants to talk about with Luke, comment on body parts and appearance of girls or for them to share their experiences with girls. Luke told us Cassie has been trying to invite herself over when his friends are here but he does not want that to happen because his buddies will not appreciate this kind of discussions either.

Husband and I talked to Anna about it and kindly asked her to have a discussion with her daughter. She blew up completely calling us and Luke names. When she saw that my husband was not giving up she started attaking me claiming that as a mother I should have compassion and understanding for a child who just wants to be accepted. I told her I do understand Cassie, but that Luke matters too and he has the right to set boundaries when feeling uncomfortable. Anna accused me of spoiling Luke and turning him into a brat and called my husband a doormat for always doing what his wife and kid want.

I truly understand that Cassie is going through a rough time, but it feels like she wants everybody to accomodate her while she does not care at all how she makes other people feel. And I strongly believe our son should not have to put up with things that make him uncomfortable or for him to be called names just because he does not feel like talking about certain topics. AITAH for this?