Can I be bi?

I love watching lesbian porn , I've had relationships with girls not anything serious though just to mess around, I've kissed girls and didn't really mind it , ive done other things with girls as well but whenever I picture having anything serious with a girl or having real feelings for them I think to myself "no way that's not possible" it's like I can't imagine that happening . I don't understand why, can anybody help or has anybody been in this situation?