Is it cheating if a guy your with looks at personals behind your back?

I had a funny feeling and so i checked the computer at my mans work that everyone uses to see what kinda **** was on there. So lately I've been feeling like I've been doing a lot, you know relationships are give and take but somehow i feel like I'm getting the short end of the stick here. Bending over backwards, basically tonight I wasn't feeling that great so I ended up going to his job and to make a long story short I could tell he had been look at personals off of craigslist and there is more details but i don't want to type till my hand hurts but is this cheating. By the way the reason I felt that weird feeling is because sometimes when we argue he would tell me he is already talk to someone else. I know love is blind but do I need to wake up and see that this is clearly wrong?