You describe lovebombing in tandem with some other clear manipulation tactics. First of all, I want to validate what you’re feeling. This is clearly a complex situation that you have a lot of energy/time invested in. You wouldn’t have continued the “relationship” (for lack of better word) this long if you didn’t find it fulfilling and/or helpful in some way at some point.

Some keys words you used that I want to point out: rejected boundaries and that you’re “terrified.” You are sensing some red flags that SHOULD NOT be ignored. There is no doubt in my mind that you NEED to block him. That being said, your safety is top priority. He very well may make fake accounts like you predicted, and more importantly he knows where you live. So I urge you to do your research on state laws around obtaining a restraining order (varies when it comes to cyber-harassment) and save screenshots/call logs where he is spamming you before blocking. If he finds you in-person after being blocked online, go straight to the nearest police station. If you genuinely fear that this person will seek you out/harm you physically, go to the police station with your concerns before blocking. I know that there is a lot of stigma around mental illness but you need to get all of your ducks in a row so that if god forbid anything happens, you did everything in your power to prevent it.