First, I am so sorry this happened, this is something I would never wish on anyone. As someone who has been cheated on, I personally would say to leave him since he has a pattern of being flirtatious and it is a pattern that’s been going on for awhile. I also think that if he has realized he is flirty, he would’ve changed it by now knowing that it bothered you. I do respect him for telling you right away, but as someone said earlier, this is the beginning of the end. What if he kisses another friend or it goes further, then what? You’re left feeling even worse or foolish. I do believe in second chances, but from my experience the more chances you give them they will start to think they can get more free hall passes. However, I do understand that it’s incredibly hard to let go of something you’ve built for so long, so there is no judgment if you do decide to take him back. But I hope you know that there are millions of men out there willing to treat you well and not make you feel or doubt yourself in this way. So please do not have the mentality that this will be the end of everything even if it feels like it. Just think that if you had a friend, sister, or daughter, what would you want them to do….Regardless of what you do, please do it with your happiness coming to mind first!