[FF] Mom’s wife

So, hear me out before I get lynched. My parents separated when I was 11, the reason being that my mother came out as a lesbian. I then began living with my grandparents while my dad married another woman and my mom went exploring or whatever, so I never had a close relationship with either of them during my adolescence. This changed a little when I turned 18, but still, I’m almost friends with my dad and colleagues with my mom, at best. My grandparents were the “real” ones growing up, so that closeness with them was never really there. Now I’m turning 20 next month and for the past four or so years my mom has been in a stable relationship with her “wife” (they are not legally married) and they live together in her apartment. I occasionally visit them and sleep over, and while I’d love to spend more time with my mom now that I’m older, I have one big problem: her wife really wants to fuck me and I’m barely handling it.