Obsessed with people? satisfaction from pretty much stalking

Well, I guess this will be the first time I say anything about this. Well I'm a female, been with a guy for almost three years. I used to know his ex girlfriend. Well I became obsessed with his ex girlfriends. Almost all of them... Then literally began stalking about three of them, their lives. Not physically, just social network, things like that. It was weird but I had some sort of desire. Well long story short it turned into one main girl I had an obsession with. I check her social network pages everyday, almost hourly. I pay attention to the people she talks to and what she does with her pictures and physical appearance., every last bit. I noticed she did things like me. She started dressing like me, styling her hair like me, make up like me. And even took pictures like me. Ever since then I became obsessed with her. I'm under the suspicion she does the same because she will hint it, by copying me. And i don't know if that's over analyzation or paranoia or if it's true
But it hasn't gotten unhealthy. I think about it all the time. I even hacked her accounts in the past, and read through every single one of her messages and all that. I don't understand why I am doing this. I feel like her intentions are just... Bad. It's embarrassing to say but I feel like she's almost evil. I don't know why I feel satisfaction from pretty much stalking her life. I'll even force myself to listen to the sake music as her. Anyway... I guess I'll just leave it there. I know this can't be normal, so I'm just wondering what types of mental illnesses could be associated with this..? I have been diagnosed as bipolar and anxiety but I'm pretty sure both have nothing to do with it... Okay, thanks to whoever takes the time to read...