I would cheat on you too. Any chick that is so insecure that she installs tracking software on a guy's pc and snoops theough his phone is a smothering, annoying, bitch. He'll ditch you soon enough. I'd guess the only reason he even keeps you around is that you have a nice ass or pair of tits, or maybe you give good head. No man wants a smothering bitch.
When he finds the software your shit will be on the curb and the locks changed. you are probably up his ass 24/7 too. Do him a favor and leave.
Well now you know why he cheats on you. You do not trust him and I am sure you have accused him of this even when he has never done anything. When you accuse him of it enough times you push him into it. So now when you open your mouth and accuse him it will be true. Leave before he throws your ass out.