i messed up big time

so i got into a relationship with my best friend from high school years ago. we were both in our mid twenties at the time and just wanted to try something new, right? it was supposed to be this amazing thing, but as soon as things started getting serious, they lost their sparkle, ya know? we lived together and everything, and i guess one day it just hit me that maybe we weren't really meant for each other in the long term. not like those epic forever kind of deals or anything. so i decided to hook up with this girl from work. she was pretty cute and all, but honestly, i wasn’t thinking much beyond a casual hookup. the thing is, my girlfriend (or should i say ex?) found out. i mean, the text messages were kinda incriminating... and now we're broken up over something that really shouldn't have been this big of a deal in the first place. but here we are. now i'm single again, trying to figure out what went wrong with all of this.