I think if you can possibly get away without the children overnight that and really talk to your DP some more that would help immensely.
Maybe have a glass of wine first.
Some moments or even a few days of embarrassment are worth experiencing if they lead to greater clarity. ATM you are in the dark, confused and unhappy.
And tbh you are totally justified in exploring this issue when you are about to be married. In fact you can use your forthcoming marriage as an excuse to open up the dialogue. Say that if you marry someone, you want to have a reciprocal, respectful physical relationship with them and if it's not possible to even speak about such matters then you don't want to go ahead with getting married because this is a deal-breaker for you. Obviously you have to be very sure that it really is a deal-breaker for you and be prepared to split up over the issue.
Don't put up with being called selfish op. You are not being selfish at all. You are setting a standard and a boundary for yourself and it's a very normal thing to want a healthy sex life. It was terrible that your DP suffered sexual abuse that has caused such damage to him, but is it fair that you suffer from that legacy for the rest of your married life?
You are within your rights to ask for more clarity. You deserve some honesty before becoming his wife fhs! But keep the questions factual and unemotional in tone:
First of all, is it a physical issue or not?
If it's physical, can it be treated? If so, would he want that?
Is the sexual abuse at the root of his ED?
If so, is he prepared to undergo therapy and use medication to treat this or not?
What would he like ideally? If there was no pressure either way?
Is a regular physical relationship important to him or not?
Would he prefer living as friends without the question of sex cropping up?
If so, is that because of embarrassment about his ED, or because of his past, or because he is just no longer interested?
Does he feel that you deserve a healthy sex life or not?
What are his greatest fears surrounding this issue?
How does he see your married life developing?
Make sure that these questions are asked calmly, without any impatience or hurt evident, and make sure he understands how much you love him.
I think it's worth a shot tbh. And if you really can't even talk about the issue, openly, never mind resolve it, that doesn't bode well tbh. Good luck.