Guys: Is there usually a reason why you don't kiss a girl during s.e.x.?

I started having sex with this guy (who I've had a crush on for two years lol) who is my ex's best friend (they aren't as close now though) and even though we don't see each other that often, we've been hooking up for the past couple of months. We've probably have had sex like 5 times so far and he has never kissed me til the last time. After I sucked his ding a ling he got close to my face and said he really wanted to kiss me, and i asked why he wouldn't and he said its because i sucked his thingy, is this really a problem with guys? I mean i used to understand why, but then as I became more experienced i didn't see a reason why that would matter.