Relationship help!!

Lately I've had dreams of cheating on my bf and then I sometimes fantasize about being with other men for a few days after. My SO is my 2nd partner and I was never able to "sow my wild oats" if you will. I thought I was getting over that little phase but then last night my SO and I had sex for the first time in a week (which is rare for us, normally we have sex everytime we're together since we don't see each other but a couple of days a week).
 During our sex we were both out of sync and sort of disconnected. Even our kissing didn't feel right. And I wanted to cry the whole time during intercourse because he didn't seem into it like he normally does and it seemed like he was having trouble finishing. And I couldn't even concentrate on enjoying it because of this. I wound up faking it and then crying in the shower. 
I don't know what to do. I can't bring it up because he gets offended easily and would take everything I say as a jab against him. 
TLDR- feeling out of sync with SO and disconnected during sex.