Dad Hooking Up With Girl My Age Who Looks Just Like Me

recently i (18f) found out through an older guy (50m, referring to as S) i’ve been talking to, that my dad is hooking up with an 18 year old girl (S is also hooking up with her and found out after he told her about me, she told him about my dad and they put together the association)

everything about the situation is so weird, not only is she really similar to me (we both school refused in high school, same interests and attitudes to relationships/sex (except i’m a virgin and she is obviously not)). but she’s also into really deranged kinks like ageplay and incest. also for whatever reason, when S showed her what i looked like she started crying.

i’m just really disturbed but it’s manifested in a kind of obsession about her. i’ve been stalking all of her socials that i can find and i can’t help myself from asking S questions about her.

i have a really bitter attitude towards her which i do feel guilty about because i’m sure if i met her in any other circumstances she would be a nice person. but i can’t shake the knowledge that there’s someone walking around my house when i’m not there, essentially pretending to be a 5 year old version of me and having sex with my father. especially considering all of our shared interests, it feels like she’s wearing my skin and i almost hate her for it.

EDIT: i understand i’m going to get allegations of this being fake since the situation is genuinely so crazy. however i feel like i’ve been a victim of the sexual fantasies of people around me and being accused of this being a fake sexual fantasy of my own is insanely frustrating. S is the only other person who knows about this and hasn’t been very validating of my feelings either hence why i came to reddit after sitting on it for so long. i would just really really appreciate some understanding.