Does your man spent alot of time on Facebook?

Ive been with my bf for almost a year. We live together his always on Facebook and if not on that playing video games I honestly didnt have a problem at first but its been bothering me lately beacuse when we were dating at first I found him talking to this lil 18 girl with a bf he would comment on her pics like bed over n shit one time I was staying over his house before moving in and he was commenting on her page just cuz she had posted something about her bfn. Well long story short he tells me he was telling her to back off but to me it seems like he like flirting with her n I wonder if he is doing that with other girls thats why it upset me so much I always see girls tryna talk to him... Honestly I never been with a guy whos more into facebook than me idk if im over reacting but it hurts when u see stuff like that posted yet he says he wasnt tryna talk to her. Does your man get on facebook alot?