Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I am very sorry to know about this frustrating situation. Could you please tell me what is your biggest fear about it?
Then if he was truly being honest about it and you trust him, you would be consistent telling him about it, to show you care and fully respect him. You would ask him if eh wants to know before telling him, that way he would choose what he prefers, while you would be fully consistent with your honesty and affection for him.
If he is being truly honest and caring towards you, he would not push this subject any further, and focus on building and enjoying a healthy and fulfilling relationship now, in your present, which is what you can and should be totally accountable for, without pushing details about your romantic past.