My current boyfriend keeps bringing up my ex, he asked me about my ex and I brought him up that one time. Now my current boyfriend keeps saying

Its your fault. If you did not have an ex this would not happen.

That sounds like potentially jealous and untrusting behaviour.
I would put the kibosh on that instantly, before he starts thinking you'll let him carry on like that indefinitely.

First say that you're willing to fill him in on all the facts of your relationship history with proof, but only once, and if, after that, he doesn't trust you or questions your honesty and integrity, tell him it will be a deal breaker and the relationship will be over.
Explain to him that, in your view, if a couple cannot trust and respect one another then there is no possibility of healthy love. So he gets this one chance to see who you really are - and after that it's up to him to show the kind of person he is.
Of course, if either of you later breaches your monogamy agreement, then you both go your separate ways.

Infidelity can be worked out and survived. Many people do it, especially if kids are involved. But it creates an incredible rift in the trust, and many couples can't or don't survive that.

If your boyfriend doesn't trust your reproductive history, make an appointment for both of you to see your doctor. Ask the doctor to show him your history of births, abortions, contraceptives and STDs. That way, he gets an accurate and complete history that can't be questioned. Then ask him for the same, you visit his doctor and hear his complete history.

If your ex was a spouse or de facto, show your boyfriend any papers that show date of divorce, moving out, financial settlements, etc. If there are kids, show the parenting arrangements, history of any conflicts and how things were settled.
Then ask him for the same with his ex or ex's.

If you still have your ex's mobile no, ask your boyfriend if he would like to meet the ex to see for himself.
You could also show your text and email history - just once and maybe do a printout.

Of course, all this presupposes that both of you prefer and value monogamy.
Also, what you both enjoy and how often you want it is also an issue for long term compatibility. And mature people will accept that this can fluctuate over time with health, age, stress, children. etc.

You need to make sure that he doesn't have double standards and is not acting from a desire for ownership and control of you.
If either of you has different values, that needs to be discussed and understood; if one can't happily go the other's way without compromise, it would be a disastrous match.
Bare in mind, some young people have experimented and learned the hard way. That kind of history should never be held against someone.

Red flags all over the place. Move on.

If he's going to be that mistrusting, then you should dump him. I understand asking why you broke up or even making a joke about it, but it makes no sense for him to keep digging it up. It's not fair to you and certainly not fair to himself.

He might have a Paranoid Personality Disorder, which is considered a chronic disability. He might need to see a psychologist.

Because he so worried you may go back he can't focus on the fact he has you now.

Ask him what he thinks of Andrew Tate, if he adores him; dump him.