Visiting his home for the first time, only to realize the full extent of his relationship with his roommate he didn't mention moved in, as well as find all his lewd acts going on in secret. Waiting at his place, sitting in a shitty apartment in the same room as the man he cheated on you with, waiting in a pang of misery until he gets home so you can tell him it's over, only for him to avoid coming home and you leaving for your own not being able to take it anymore. Talk to him through IM as he openly admits how he lied to you this whole time, as non-caring as possible. And then that's it, feeling no resolution.
Last time I invest as much as I did half-heartedly in someone, anyway! All in good experience I suppose, haha.