If he was a cheater and cheats on you when you guys are supposed to be monogamous with each other (assuming you didn't just assume you and him were exclusive)he will always be a cheater unless he wants to change his behavior, if when you met him and he cheated with you its only a matter of time before he moves onto the next and cheats on you with her, if he is not a father to his kids before you meet him and then you lay down and have kids with him then guess what he's not going to do right by y'all kids either. There is a basic rule that most people don't remember when they are in the midst of a emotionally charged situation, that rule is YOU can not force a person to change their behavior! There is nothing you can say nor do to make a person who doesn't want to change, change. Many people make the mistake of thinking that they can reshape a person's habits but unless that person specifically request for you to help them change and they are open to changing their behaviors the changes won't take effect and you will just be frustrated and upset because the outcome you want will not manifest itself.
Why waste all that time and energy on trying to manipulate another human being?
Another fundamental rule that I state often is NO one can do anything to you without your permission. If you repeatedly let someone lie to you, use you, steal from you, take from you and you don't stop it or remove yourself from said person/and or situation then you are being a willing participant in your own victimization. In life there are exceptions to almost every rule however short of being incapacitated, physically and mentally unable, and just flat out emotionally inept no one should be pulling your strings and making you dance to their rhythm if they are may I suggest you invest in some scissors and cut the strings already, what are you waiting for?
This Valentines day ladies if he isn't making the grade then cut him loose, married, dating, engaged whatever if he is just making you so miserable to where you hate to be in his presence let him go and learn to love yourself a little bit more. Give yourself the gift of self love this valentines day instead of misery its a gift that will keep giving and bring with it the satisfaction of knowing you are finally being treated the way you want to be treated by the person that is most worthy of your love and that is one's self.