<human>: I have been dating my wonderful girlfriend for over a year now, and things couldn't be better. The problem is that about a month into dating, I was at a party, and while I was drunk, another drunk girl that I sort of knew kissed me for a few seconds before I realised what was happening and pushed her away and told her that I have a girlfriend. It was my fault for putting myself in this situation and I'm fully aware of the fact that I fucked up. 

I would have owned up to the situation immediately if it wasn't for the fact that I've known my girlfriend for a while before we started dating, and due her parent's ugly divorce that involved infidelity, she is VERY strictly monogamous. Maybe that is just an excuse for not wanting to tell her, I'm not even sure at this point. The guilt has been killing me, and the fact that I love her and see a future with her makes the guilt even more painful. I am contemplating whether I should just tell her what happened, but it seems like a selfish act to hurt her in order to relieve my own guilt. However, I do feel that if she were to find out some other way about what happened, she would be even more hurt. What do I do?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Got kissed at a party early in the relationship, but haven't told my girlfriend. The guilt is eating me up, should I tell her?