Overthinking ?

Last night my significant other and I had sex and after we ate and watched a movie he went home and on his way home he calls me out of no where and asks me “don’t get offended but I just want to ask you a question?” And I said “yes?” And his question was “are you have sexual relations with anyone else?” Obviously I’m am 1000% loyal in my relationship with him and I would never cheat.... but I kept asking him why the vquestion? What’s bothering you? He said it was just a question.... that it wasn’t that big of a deal he just wanted to know.... but honestly I don’t believe it! You don’t just ask that question to ask unless your thinking about something else..... I got some advice from a really close friend and she says that maybe he’s cheating that’s why he asked.

Guys? Ladies? What do you think I’m i really overthinking? Why would anyone ask that question?