“Nice” guy bullshit

So (very) long story short, my guy friend from college (who admitted he liked me our senior year when I still had a boyfriend at the time, and I told him I only saw us as being friends) has been harassing me ever since I started talking to another guy. It has been almost 2 years since he told he had a crush on me and I was very forward (and nice) about saying I didn’t feel the same way. We still hung out with all of our mutual friends our last year at school and he even would talk to me about other girls he was talking to and I would give him advice (I assumed he was over me). But apparently I was wrong. He has been texting me paragraphs about how much of an awful person I am and how I’m a bitch and “this is how you treat me after I’ve been so ‘nice’ to you”(ugh. Vom) non stop at random times. He is acting like I owe him a relationship because he was nice to me (typical “I’m a nice guy” behavior) He somehow finds out when I am over at the other guys house (they live relatively close to each other) and even went as far to Snapchat all of our mutual friends in a snap group (that I’m in) about how much of a slut and a bitch I am and I got to hear all my “friends” agree with him (they all see him as this sweet puppy dog type of a guy) I’ve been having major anxiety attacks to the point where I had to leave work early one day because I had an awful panic attack. This has been goin on since January. I feel like I’m in fucking high school again and we’re all in our 20s. What the fuck do I do because I’m borderline about to drive to his house and beat the living shit out of him and tell him to leave me the fuck alone.