Why was my boyfriend twitching?

Please, no rude comments. I know I made a dumb decision. I am on cycle day 14. I am 16 and my boyfriend is 17. my boyfriend and I had sex which was our first time. It was unprotected and before he got up he slowed down and started twitching like he was being electrocuted does that mean he was cuming while he was still inside of me? I asked him if he pulled out he wouldn’t answer me