Wrong or right? guys your opinion is needed and girls too=]?

well im 18 and i went out with my ex for 9months and he broke up with me for god knows what reason because he doesn't even know why. anyways a little after a month i started to receive an enormous amount of attention by guys. Truly it felt very empowering. i started to gain my social life back and i started to hang with a close friend again ( a cute friend of mine since we were little) =] and we started to blaze and do all our senior events together. When it came to prom we got drunk and had and later on the week we did again but sober.The best thing was that their were no strings attached. Then All the sudden my ex comes back apologizing and wanting to work things out. im not ready to give up my fun being single ...but I do still love my ex and never stopped and he was a very good boyfriend to me...but if he finds out i had with someone else !! he will disappear.... anyways what he doesn't know wont hurt him right?? or is that more of an excuse?