I'd go with the legal retaliation. If you can get his ass in jail, then his payback will be all the ass pounding he gets.

To avoid problem with the GF - Anonymous tip to the police. You need enough information to give them probable cause to search/arrest his ass and a reason to know that the information you are giving them is reliable. Find out some more info about his drug stuff, like when he makes a transaction or something and then narc on his ass. Actually, if he ever drives around with that stuff in his car, that's the best b/c of the automobile exception to the 4th amendment - that way his rich ass can't hire a good lawyer and get out of his jail ass pounding.