I attended a wedding with my current gf and my ex-gf was also in attendance -- we were all very friendly and now I can't get my ex-gf out of my head.
Was it the wedding that had to do something with it?
No, it was just a stupid social convention
You are probably just a little tender from the break up with your ex still. The emotions are still raw. You should stay faithful to your girlfriend!
That's what I didn't want you to say.
You're already with someone so it's cheating to think about your ex. Hw would she feel if she got to know about it? You need to get over your feelings.