Friend
Welcome to SI, and sorry you have cause to be here.
You are correct that carrying on into a relationship with that baggage is doomed. I know being honest might risk your relationship, but it would never have been an honest relationship without that disclosrure.
I want to suggest one main thing:
Be truthful and honest about what happened AFTER the two of you decided to be together.
Like… he has reason to know if you did A or B with Jack or Joe. But he doesn’t have any more right to your full sexual history than you do his.
Keep in mind that anything you willingly hold back can cause immensely more damage a year from now – if discovered – than it might now. Trickle-truth tends to be the real killer.
I don’t know your past, but if we imagine this scenario: If you told him you had been intimate with 2 men, when in fact it was 3, then letting him know the truth NOW is likely to cause less damage than learning a month from now that you kissed someone.
Let him know why you are being honest. That you care for him and envision a life together, and that needs to be built on honesty. If this kills that hope, then so be it.
Ask him how you can assure him he has the truth. Offer access to your phone, media… whatever he needs. Offer to take a poly, hypnosis…
Let him know that you are open to him asking anything, and that you realize that if he opts to remain with you it still allows him to ask and question. You would hope that with time his need lessens, and that over time trust can be built.
"If, therefore, any be unhappy, let him remember that he is unhappy by reason of himself alone." Epictetus
