There must be more to this story. Why are you concerned? If you hit them in their rear, he yelled and drove away, how could he sue you later? You said ins info was not exchanged. Were licenses/names/phone numbers exchanged? Did he write down your plate or take your photo? Do you have his information? Tell us the rest of the story.
Absent a marriage or a written agreement to the contrary, your boyfriend will not become entitled to half of your existing possessions. Whether he will be able to stake claim to anything purchased by the two of you during his tenure at the house is another question. Good luck.
The others are not wrong, but to me this sounds like more of a scam than anything else. And, how does creating a scenario to help a buyer get approved amount to anything less than bank fraud? Just saying...
You cannot lock someone out of their home without a court order.
Whether they will owe you mortgage payments will depend on your agreement.
If they do not want to be in the house, why do you need to lock them out?
You need a real estate attorney or a civil litigator with real estate experience.