PTSD from a FWB...? (May be triggering)

From February to November of 2016 I had a friends with benefits relationship going on. I had already known the guy for a year, we became friends & one day we just kinda had sex. We agreed that we would be FWB & nothing more. Around June of that year I realized I had a crush on him & it was around that time where he started distancing himself because he had found a potential love interest. We took a 'break' from June to November. It hurt because he was pushing me away & I still had feelings for him.

The day before Thanksgiving he called & said that he needed to talk about something important. I agreed to go for a ride with him (driving around helped him stay calm when letting his feelings out). He picked me up at my place & drove us to our usual hook up spot about 2 miles into the woods where there was a beach not a whole lot of people knew about. He parked his car. I knew what was coming & I told him that I had a bad day & wasn't in the mood. He kept asking me & I kept saying no. Finally he told me that if I didn't have sex with him that he wouldn't talk to me anymore. Me still being naive & having a huge crush on him I just let him do whatever he wanted to. I didn't say "yes" but I didn't say no when he started, he didn't force me but I also didn't make him stop. I didn't want to have sex with him at all. He was a lot rougher that night & it hurt. But I was stupid & didn't want him to stop talking to me so I didn't say anything. After he was done he drove me home & dropped me off. I showered, crawled into bed & just cried... We ended up getting in a huge fight about 2 days after the incident & he blocked me on everything.

Fast forward to January of 2017, I get into a relationship with this amazing guy. But sex since that incident has been difficult. It usually ends with me having flashbacks of that night with my ex-FWB & me crying hysterically with my boyfriend asking if he had done something wrong or if he had hurt me. My boyfriend feels bad & I feel bad because it's not my boyfriends fault; he didn't do anything to hurt me.

I'm stuck. I'm in a position where I feel I need to tell my boyfriend the reason why & I don't know how to explain it to him. It doesn't count as rape, right? I didn't say no, he didn't force me, I didn't tell him to stop even when it began to hurt. I just shut down while it was happening. How do I go about fixing this issue with the flashbacks? How do I tell my boyfriend?