I'm obsessed with my boyfriend's ex
What led to your obsession?
I was obsessed with her before he became my boyfriend, however, now that I'm with him, it's even worse.
It's wrong to obsess over other people, but it can be understandable at times. If you're feeling committed to your boyfriend, whatever lingering thoughts you have about his ex should fade in time.
I'm addicted to her tits
It sounds like you're not ready for a heterosexual relationship. You should discuss this with your boyfriend. If he's not inclined to be patient while you explore your sexuality, it would be best if you parted ways.