Dunno man, I am friends with ALL but one of my ex's. I am even friends with some of my ex's ex's.

one of my best friend is an ex, ex1. Another, ex2, is God father to my children They are both in my life pretty much daily.
We are ex because it didn't work, there was nothing compatible over the long term. Any initial attraction fizzled out months after we got together. That was 12 + years ago.
Now it feels like a sibling relationship..the thought of being intimate with him creeps me out, but I am comfortable enough in his company to share a bed if there isn't any space on a visit., as I do when we visit my brother.
It's difficult to explain unless you have experienced it, how your feelings and emotions can shift.

Now, years on I have another relationship, and he has been great. Although he has no experience of it, and a terrible track record with his ex's.
For him it comes down to trust, he has absolute faith in me. He knows I adore him. And believes that there is nothing between me and my friend.
He has hung out with us enough to see us together and how we interact .
He does however dislike r ex2 (godfather), but that is down to ex2 being a **** when I first met my fella.

In this instance, not accepting my friends would be a deal breaker though, I would never ditch a friend for a partner, if the friendship was established first.
Unless of course there were obvious signs of sabotaging my relationship. But that is a different topic.

It definitely needs talked about, to figure out where both sets of boundaries lie, and wether a compromise can be reached.

Best of luck, really hope things work out for you.