Legally you wouldn't be allowed to use the names of anyone that didn't give u permission...otherwise you'll face all kinds of slander law-suits by people not wanting their private stories and info put on the web for the world to see.
No way the site would work unless both sides agreed to vent their trash in public...which is unlikely from the dumpee or whoever looks "bad" in the particular situation.
All it'll take is one pissed off girl or guy who feels they've been humiliated on the web with their name mentioned and you'd find yourself tied up in expensive law suits. Personal privacy rights trump your right to make a profit unless the person is a public figure like a celebrity...and even then its dicey unless what's said can be proved. (hence all the celebrity lawsuits against tabloids claiming this and that). With non-public figures you'd be shut down imo.
Not worth the trouble unless maybe you changed the concept to have people talk about their exes 'anonymously' where they couldn't be identified.
BFM