From my point of view, it’s not important that your boyfriend once loved another. What’s important is that he learned from that experience and now has chosen you. He loves and respects you enough to limit intimacy with you to kissing and cuddling. He’s sure enough about the relationship that he is talking about a proposal.
Your jealousy and worries are not about him or his prior girlfriend. It’s about you. Your boyfriend is over his past relationship but you’re not. I’m sure there are men who, like you, are waiting until marriage to have sex. Your choice is to either break up with your boyfriend and look for a man who shares your convictions or to come to terms with your boyfriend’s past. He can’t change what happened. You can change how you think about it. Or not. It’s entirely up to you.
If you do want to try to make this relationship work, I urge you to seek out a therapist. “Confronting” your boyfriend with your feelings isn’t likely to be helpful and will probably only lead to arguments. What, after all, can he do? He’ll protest that it’s over. You’ll talk about your feelings. And around and around it’s likely to go. A therapist might be able to help you confront yourself instead. You owe it to yourself and to your boyfriend to work through your feelings. If you marry him without doing so, it is likely that you will sabotage your chances for a happy future together.
I wish you well.