He's Jealous Of My EX!

When suspicion gives way to delirium!

Just like Michael Douglas and Glenn Close in “Fatal Attraction,” the fertile ground for jealousy can grow very quickly.
It doesn't take a lot of information about your ex to spark deep interest and instil deep jealousy.
The last thing your boyfriend wants to think about is that another guy has been with you (whether it's regarding sex or just dating). Considering that someone else may have touched you or just kissed you, can literally make him very uncomfortable and understandably here, we are talking about healthy jealousy.
However, looking dignified and detached from our past, remains the basic rule.

Jealousy is a cruel mistress!
But I want to say that if, however, you are reading this article, it is not a coincidence and whatever the problem is in your relationship, keep in mind that love does not cause pain.
Have you had a sexual history with your ex that was a great experience? 
If so, your boyfriend might have a hard time dealing with it. But this is something he will have to accept. Yet not hiding anything from your partner might seem like the best proof of love, provided you perhaps avoid certain details.
Whatever happens, saying nothing is not the solution, or your past will catch up with you sooner or later.
Moreover, to say nothing at all to your partner would be a real aberration and a terrible lie by omission...I grant you. However, it will be useless to try to reassure him or to reason with him because his anxieties and his jealousy are irrational. A very simple technique may be to give him as little information as possible to compare himself to your ex. You should also know that for some men, it is easier to have a fit of jealousy than to make a declaration of love.

Do not let that happen…
Don't you dare let someone else throw your past in your face or hold it against you, especially if it's ancient history.
He has to accept you for everything you are ... he has to accept you and your past. And that says it all. That doesn't mean he has to like your sex history, of course, but it does mean he can't hold it against you. It's completely unfair that he wants to go out with you and then start knitting details from your past. That could sound like unhealthy jealousy.
If he keeps talking about your past, be honest with him that he's going to have to come to terms with everything about you if he wants to date you. Setting healthy boundaries for yourself very quickly doesn't let the situation and resentment set in.

Tell him he has two choices:
•    You two separate
•    You two stay together .... but he will have to come to terms with your sexual past. And, to never use it in an argument.

If you have chosen to change the way you "love freely", you are doing what is right and that is what matters most. There will be no point in trying to reason with your partner, because keep in mind that he is intelligent enough to understand, but obviously not emotionally mature enough to stop hurting you and making you suffer. It is therefore useless to try to reason with him.
Maybe you can rethink a possible future with him if he decides to do some work on himself. It would be a shame to position yourself as a long-term victim of co-dependency of the narcissistic pervert, who, whatever happens, will dominate your past and present life and will leave traces in the future.
If this relationship makes you suffer, save yourself while there is still time!