I also had a similar problem with my boyfriend and fb. We both have it in our status that we are in a relationship with one another, but I don't know if he knows this or not but I can see when he comments on other girls', that he doesn't know but added anyway, pics. The girls are wearing little to nothing and he always says something like 'sexy pic', I see you',' looking good.'
Takes notes from me, if you don't feel comfortable in the relationship(whether it's his fault or not) then just leave. It's really not worth it, honestly. And please dont let social networks run your life.