If she's in a relationship but could be intimate with you, that
may signal that there is some issue in her relationship. it's not
fair to jump ship if she indeed has problems with her bf. She needs
to work it out with him. going to someone else for comfort is going
to hurt her bf (imagine yourself in his shoes). To be fair to him,
she should work out stuff in the relationship before contemplating
other options.
After being intimate with someone, there is some exchange going on.
Even though it isn't evident, there is some part of you given to
her and vice versa. Afterall, you've shared something so intimate
with each other. Your feelings for her could have developed from
there. But without having been intimate, what do you like about
her. is she someone you want to be with. I must add though that it
may difficult for you to be objective now.
Even if she leaves her bf, it does not mean both of you should
together. After the end of a relationship, we should have some time
to recover. it's like sickness, but of the heart. We also may want
to think about what happened in the relationship so that it wont
happen again. If she starts a r/s with you right away, what
guarantee is there that she wont let the same thing happen to
you?
I know you have strong feelings for her now (and also because you
have been intimate), slow down and think things over. any mistake
will be emotionally costly!