I hope this still counts, even though it was a mutual breaking up!
Meet this guy through a friend. Seems pretty cool, we hit things off, after a few weeks of constant hanging out and traveling back and forth we decide to be boyfriend and girlfriend.
Found out he's been into heroin since his mom passed away last New Year's, but he's been clean for a while. His mouth was a trainwreck so it made sense. Also found out he's been charged with assault and if he's caught with a weapon it's straight to jail. Awesome. Should have left then.
Later I introduce him to a family friend who used to live with us with her four young kids (2, 4, 9 and 11) when her husband beat the shit out of her and she was looking to get out of the relationship. Ex-junkie, was pretty heavily into anything she could get her hands on.
He starts talking about starting to shoot up again and I tell him if he does it's the end of our relationship, and he can ruin his life while I'm not in it. All is well for the next little while.
Found out later that he cheated on me with the junkie mom while they were snorting and shooting up all night and decided not to tell me until a few weeks of being together, all over text. At first he says he wants to keep the relationship going because he has something "solid" with me and not her, and then goes on to say it's over because I'm a bitch because I didn't want to be a swinger. Fine, the feeling is mutual, good riddance.
He basically tells everyone that he left me because all I did through the few months of our relationship was cheat on him, I was nothing but a bitch and a cunt and our relationship was nothing, and even got his hands on my friend's gun with the intention of "shooting me in the fucking head". Had to be told by said friend. Said friend took the gun back. Thanks, friend.
TL;DR: Heroin addict cheats on me with another heroin addict, tells my friends he left me for cheating and then threatens to kill me for calling him out. By far the worst way I've been broken up with 0/10 would not do again