It shouldn't...

Its unfortunate, but it does

Lots of things happen. Just like this FML being posted (it should have been posted, and it is).

I was waiting for someone to say that!

I was going to ask this!

My favorite scene XD

Damn it! Beat me to it!

Time to run then lol

You can definitely tell whether someone is looking at you or at themselves in a mirror. If their eyes didn't meet, he was looking at himself.

*The only constant is you.

I agree with this. It's a form of voyeurism but instead of peeping on others it's looking at yourself. This might not be the case either, it's very likely that he was curious as to how he/you both look(s) while having an intimate moment. I've looked at my boyfriend's and my reflection before for both of the above reasons. As weird as it might sound, I've also fantasized that I was another women while my mate had sex with me. I was able to do this by looking at my reflection and pretending I was a third party. Everything I've mentioned could be the case. I wouldn't worry too much about it. If you catch yourself wondering or worrying you could always just ask him about it. Hope this helps OP.