Facebook causing problems?!

Tru
So yesterday me and my bf got into it because I posted a selfie on fb. Which his mom liked and commented on. Cause she's my fb friend on there too...anyway a guy I use to know commented calling me sexy. Now I saw it and didn't say anything back to this guy. Now I don't have no communication with this guy at all. He's just a fb friend. My bf got upset because I didn't tell him about it and because I didn't tell the guy I have a bf. I just didn't respond. So he got upset and started arguing. Now my question here is should I have said something? Is it really that big of a deal? He said I was trying to hide it from him but in reality I gave it no thought. Like it's just a comment. My bf is my friend on fb like I just don't get it. Oh and he's mad that his mom seen it too.