First, understand you are not marked for life. You never had a commitment to him in the first placed. You had a right to date the other guy. Some guys are jealous and don't like to hear that you dated another guy. That is past history. You don't have to be sorry about that . You never betrayed him or destroyed any trust that he thinks you two had as far as I can see. Do you agree? So forget about being marked for life. It isn't  so. He now drops the bomb on you--I am thinking about marriage, but--note the but, you  have cheated on me and I can never trust you anymore. So does he really want to marry you or not? Sounds like he has found an excuse to not marry you. The excuse is something you never done in the first place--betray him in a committed relationship that never really existed. Has he go you confused? Maybe he thought you were in a committed relationship but if you were he should have told you about it. You are allowing yourself to feel very down and depressed because he is telling you that you are the bad one in this relatonship. I guess he never does any thing wrong. He never left you in an unclear relationship in the beginning; if he loved you he would have made it clear. He is going back on you and making you the bad person. I wouldn't take it! As others have said, there are other good men out ther; if he won't stand up and treat you right and quit the blame game, walk away. Don't let any man put you down and allow yourself to feel worthless and depressed over his comments. Llife is too short to live that way!!