Dating a known to cheat guy

I am with a guy who knows how much I love and care for him and knows I am ready to settle down. This guy is known for cheating in the past with his ex girlfriends and now he is talking to his ex girlfriend. He said when I first met him he thought of his ex as just a friend and that he never wanted to hook up with her anymore. Then one night shortly after he said that he saw her at a restaurant with this guy she was talking to and got so pist she was with him and started callin her a slut and etc. then they talked a little here and there in the beginning then stopped. Now she just broke up with her man now there back to talking again. I’ve caught him in lies about chilling with her once that I know of, they were headin up to a car dealership cause she wanted to look at a car and he went with her to look. Then I keep finding they are talking all the time now and have meet up a couple times either to drop the dog off or to pick something up. anyways he says there just friends and I have nothing to worry about cause he loves me and only me but has said he wasnt 100% in the relationship with me cause I have a child and it still comes to his mind sometimes and gets scared. we have been together now for a year. what could be going on here