Deal with that however you want but do not forgive him, I promise he will do it again. (Tho if you wanna get some revenge I would stay with him just for a tiny lil bit longer just to make sure I turn his life upside down before leaving him. I would just do small things like "accidentally" forgetting some blue cheese in the back seat of his car, dropping his phone and cracking the screen, putting nails under his tires, washing his favorite clothes with all together so the colors change, o and with the blue chesse you can also smear it in hidden places around his house and specially in his closet make sure it's humid and that the chesse isn't really visible so the mold looks natutal aaaand if his best friend(or a close family member) looks desent enough and you are feeling up to it you can do some real funny shit... But anyways just make sure you move on after fuck up all his shit (๑•ㅂ•)و✧)
This might sound pessimistic but, if it was one sided, just have your mourning time and move on, cause if bro didn't know nor feel anything then it'd be unfair to just up and get petty. One sided feelings are not easy to receive.
Now, if you tell me you guys had a situationship and still did that, yeah do some petty stuff and, again mourn and get over it but do as the other person said. Don't ever get with them. If they cheat once, nothing stops them from a second time and so :/

the guy i love just texted me saying he had sex with someone else i’m so heartbroken