Before & After

Me and my girlfirend have been friends for 3 years before we started dating, we have now been together for 3 months. Before we started dating we were together with a mutual friend at a long weekend getaway. One night at the hotel me and her kissed for the first time, and I was told later that she liked me during that time and a little bit before. Anyway the story goes that on that night she also hooked up with my friend (which I dont mind - as it was all a bunch of fun and he's a trusted friend) but later in the night about an hour later she hooked up with another bloke who wemet for around 30mins. Im angry because if you like someone you should show that to them and not say "I thought you didnt like me." If you like someone should you not wait to see how they feel? You cant just think something and expect it to be right. We are deeply in love now, but I hate thinking about that the first day we kissed which was "really special" was shared with two others.