Welcome back ladies and gentlemen of the internet. You can know someone for years, spend all your time with them, even live with them, until one reproaching day unveils a curtain you weren't prepared to digest. When the rose colored glasses fall off and long ignored verisimilitude appears, it can be jarring and traumatic. Honesty and trust predicate any healthy relationship, and their foundation is what keeps couples together.
This brings us to the Reddit thread. The original poster (OP) is a man who's just hastily, albeit rightfully, broken up with his girlfriend. After being an afterthought invite to his girlfriend's male coworker's party, his night makes him increasingly embittered towards her. When the party ends and he goes to look for her, he's told by the coworker that she's left for his afterparty, in which the OP isn't invited. He spends all night waiting up for her, but you'll have to read the full story below for all the juicy details.