Having flashbacks...what do I do?

**KINDA LONG - SORRY**

So I dont really know how to go about this so sorry if I word it weird or whatever. I'm really confused rn.

A little over 2 years ago I was occasionally seeing this guy who I'd known for many years. Needless to say I was crushing real hard and he was using me to say the least. It was basically sexual. We only had penetrative sex once which I later found out resulted in him giving me chlamydia (which according to a mutual friend he tells people that I gave it to him. whatever). But we messed around every once in a while mainly him giving me oral etc. But the last time I told him he wasnt going to put it in without a condom. I refused to do it after without one (should've left his ass sooner, I know. I was stupid). Well to put it simply he didnt care what I wanted. He kept trying to insert it and put his whole weight on me so I couldn't move. I was so scared I started freaking out and basically screaming at him to get off of me. He eventually did because I "killed the mood". I haven't spoken or seen him ever since then because I was so terrified. I had known him since 6th grade and he used to be a close friend. I was shaken.

So flash forward to now. I'm with a great guy and have been for the last 2 years. Hes amazing and I'm really lucky to have him.

Here's my issue: I have depression and anxiety already so I'm very emotional and such. I've been like this since middle school so I'm used to it by now. However a couple of months ago there was a guy at my work who started harassing me and the other girls. It got so bad that one night he chased after me from my work place. It freaked me out and I avoided people for a while. That's when this all started. I started having flashbacks of that night with the first guy. How scared and terrified I was. The guy at work reminded me of what happened and I was freaked out. Eventually all of that got resolved at work. But it's been 3 or 4 months and I'm still having flashbacks. It scares me so bad that sometimes I just start crying hysterically because of it. I dont know what to do. My boyfriend is new to all of this and tbh I haven't told him about what the flashbacks are about because he hates the guy so bad. I guess what I'm asking is how do I tell him about this because I dont even know how to start this conversation. And also what can I do to make the flashbacks stop?