How do I know if the woman (lesbian) I'm seeing is commited?

I'm 25, she's 32. I really like her, in fact I think I love her. She says she loves me and wants us to get a place together. I have a lot to lose if this doesn't work out. I've been in a hetero relationship for over a year and am meant to get married next year. I didn't wish this upon myself, it just happened. I've never been unfaithful.I can't stop thinking about her though. I tell myself that I'm stupid to leave this relationship for a woman, but the hearts stronger than my head. I fell for her at first sight. I think we have a soul connection. Please....advise...have you been in a similar situation? My partner has always known I was bi, and accepted it. Now I think I'm a lesbian, I'm sure of it. I've had plenty of girl and boy friends.