WOULD YOU TRUST YOUR BOYGRIEND OF FIVE YEARS IF HE DID THIS?

My boyfriend and I have been together since 2006. He started a job in 2008 after talking to a girl at his gym who set him up at a part time mall job that sells sunglasses. In 2009 we broke up for a month and, after we got back together, this girl was texting him about work calling him "babe". I was suspicious that he got with her while we were broken up but I let it go. We have been together ever since, but on New years eve he had gotten drunk. His mom kept texting asking where he was so I finally answered her to let her know he was ok. I noticed there were several texts to this same girl from ealy that day starting in the morning. The last one said "Nikki... you're the sh*t! I love you city girl!" (I guess because she also works in the Soho NY store and also with him in NJ) He did this at 1:55 on New Years eve while I was hanging out with his friends then he appeared in the room a minute before midnight. She didn't answer the last text I saw, but I feel he was obviously flirting with a girl he had feelings for. He didn't text ANYONE else and we both have friends of the opposite sex that I know are really just good friends, He apologized the next day and says he was drunk (but he text her way before he started drinking) and when I bring it up he says "get over it". I can't. I am thinking of ending is because my feelings and trust of him have changed. opinions please!!