Am I being a psycho

So last night me and my bf were really drunk and we were talking about the start of our relationship (we have been going out 2 years). Somehow we got onto the topic of other girls etc and be said when he first met me before we were official in the first week or so he kissed other people and stuff. It was the first I had heard of it and i supose it's not really any of my business as we just met at the time but it upset me to think about it. Am I stupid or crazy to get upset about this? Please help?