What do you call it when you feel this way??? 10 pts?

I'm in a relationship with a woman, who I love, right now. The thing is, I recently saw my first love at my school (college) and we started talking. I was right back to 8 years ago when i first fell in love with her, and I had this warm, serene feeling around her. But I would NEVER want to be with her, EVER, and I love my gf that i have now and would not trade that relationship. But why did i feel that way, and why does it make me feel different than i do with the gf i have now - almost happier - even though i don't want to be with her? What is that? Like, what would you call it?