Crying during sex

I hadn't seen my bf in almost a week which is normal from time to time. But this time....? a couple days ago he came over to stay the night with me, he was doing his thing down there and everything was pretty normal. Then as soon as he entered me I felt my eyes welling up. It didn't hurt or anything and I definitely wasn't sad. I tried wiping the tears away before he noticed but they kept coming. He obviously could tell and started kissing/wiping them away. Idk I guess I really missed him this time and today he asked why I was so emotional and I don't have an answer for him.  It's just something that happened. He said he was thrown off by it and didn't know if he should've said something