15 months is a long time in a relationship, has she ever given you reason to believe that she wants to cheat?
I'm gonna tell you again. Have some confidence in yourself. Believe in yourself. If you believe in yourself, others will as well.
There's a book you should consider reading, Stephen Covey's The Seven Habits of Highly Effective People, while it was written as a business book, it's primary purpose, is to help you get what you want out of life.
It's good that you were honest with her and expressed your concern. Did she answer your question? Then drop it. If I were her, I'd get a little bit frustrated by your asking, cause it would make me think you didn't trust me, until I give you a reason not to, you have no reason not to trust me, remember self fulfilling prophecy. If you think that she will remain faithful, and you tell her that, trust her. What were some of the things that you approved or disapprove of. I surely hope flirting wasn't on the disapproval list.
Flirting is harmless fun, flirting with someone doesn't mean they are going to end up in bed together. It's just flirting.
