Giving 2nd chances, do they really change?

Been with my bf for over a year and two months ago I found he had created a fake Instagram and was talking to other girls and exchanging pictures. Also was watching porn and masturbating at least three times a day. After this happened Igave him another chance and I have a device on his phone so I know everything he does & all that nonsense has stopped. At the time this occurred I was working overnight and working all afternoon so we never saw eachother and also never had intercourse which is why he claims he took the actions he did. He pleads for forgiveness and how sorry he is and he will never do it again (which he hasn't) but I still question myself and now I compare myself to any girl in the room. I'm beginning to think I'm not the only one he wants but he does nothing more than try to show me I am. I NEED HELP AND ADVICE. Anyone ever been in this position? Do you think someone can really change? I am so in love with him I don't want to leave because I really think he can change ... I JUST DONT KNOW!! HELP