Why do I (22F) break out crying almost every time my boyfriend (24M) has sex with me?

My boyfriend and I have been together for a year and a half, and almost every time we have sex, I break out crying. It’s not after they’re finished, it’s during intercourse. Sometimes it’s loud and I can’t control it and sometimes I can control myself enough to cry silently. I don’t know why it’s happening. Sex is good and enjoyable the entire time, he’s gentle and makes sure I’m okay throughout the process. It’s embarrassing, because I don’t know how to explain it to him.