There are two issues:
(1) How do you get paid, and (2) How do you get rid of the home.
If the boyfriend actually has good title, then terminate the (existing, month-to-month) lease for “all occupants.” You can also follow your state process for abandoned property and it should allow for “scaring” the true owner out of the woodwork, whereupon you can present a bill for the back rent and/or “Storage” fees. If you bring a bill for $5,000 in storage fees (or something like that, see a lawyer maybe) into Small Claims Court you can probably get a judgment, then execute that judgment on the titled property, and then you will have ownership of the home and can evict him as a holdover tenant with no rights.
Do you want the home or is it an eyesore? If the latter, then you can demolish it as soon as you have an order, which a judge should give you if you follow the proper abandonment procedures. (Once it’s yours you can dispose of as you choose).
Also in theory.
In practice, you are going to have to either chase the guy off without disturbing the peace, then deal with the home as abandoned property or squeeze money or title to the home out of him if the home stays.
You may be best off giving him $500 (and forgiving back rent) in exchange for giving you the home and him leaving & never returning (forfeit all rights, etc) Consider it purchasing the home for the amount of back rent plus $500.