Please reassure me

I've cared for many people with anorexia / bulimia in the hospital setting. They are the hardest people to help because they are driven to continue down that road , no matter what. They'll go along with treatment while you are watching them, then immediately go into reverse when you are not there. I'm amazed that your son has been able to sustain two relationships and fatherhood . I can't offer any help - your son has to seek help himself and there is nothing you can do to change him. good luck.

Realistically, unless he decides he's ready to seek help you won't be able to do anything. I understand that it's hard. It's very hard.

The reality is that the underlying issue isn't about food. It never is. Until he is ready to handle the underlying issue there's not much you can do. All I can suggest is being supportive and not making food a battleground. Don't pressure him to seek help as it will likely make him even more resistant.

I'm afraid that until he admits that he has a problem, there's not much you can do to help him get treatment. I trained as a mental health nurse back in the 70's, and saw the same patients suffering from anorexia admitted repeatedly. We got them to their target weight, discharged them with follow up appointments to see the psychologist, which they rarely attended.
It must be worse for a boy/man as it is seen as a predominantly girl's disorder.
All you can do is offer your support, and try to get him to see what he's doing to himself. Anorexia/bulimia makes people deceitful, manipulative and devious, and he will have no idea how to help himself.
Be there for the family with your love and support, until he realises that he needs help.

It is hard, I don’t know much about what you’re going through, but don’t give up on your son. He probably doesn’t understand why he’s doing what he’s doing, and if he feels he has lost you as well.

I’m not very good at explaining what I mean, just please, stick with him if you can

I have no experience of this illness so can offer no practical advice or personal comments.
I am sure that you will have explored all the online and real life support groups and charitable/health organisations that are there for families of sufferers.
I regret all I can offer is my sympathy for your difficult situation.