You think your boyfriend is a border line sociopath what do you do to help him?

You start by recognizing that he has to be the one to seek his own help. If your suspicion is based in the fact that he's been abusing you, then you can help him by getting yourself to a safe space and reporting his behavior so that he can be held accountable and, possibly, compelled to undergo a psych eval and treatment for his abusive behavior.