Move on.
I got dumped by some little penis who met someone else online, chatted her up behind my back and got her to pay for his air fare to the US to see her, and I found out on the day he was going. Then I found out he'd been banging a barmaid before then, while telling me he was at work. THEN I found out that the girl who was hanging around us on the night we met, was his gf and he'd told me they'd split up!! Hadn't told her though!! So I typed up his personal journal on the Internet and phoned his mother and told her she was a fat ho who'd raised a worthless worm, rang the American woman to tell her what was heading her way, and I moved the fuck on.
Petty revenge is sweet though. My first bf cheated, so I poured baby oil in his shampoo (we shared a house). The more he washed his hair, the greasier it got. The greasier it got, the more he washed it...hilarious. I did eventually relent when he moaned about it before a hot date.
Still best mates with that dude though, 25 years on. Sometimes, it does work out. We've cried on each others shoulders many a time since.