This is going to sound weird, but I'm not sure I had difficulty accepting, because, as I say, I had a history of not feeling well.
So I'd spent a long time thinking I must be stupid, lazy, or a hypochondriac - or some combination of all three!
In a way, it was a relief to find out what it was, and that it wasn't some terrible character flaw, or even mental illness. Although I do struggle with the knowledge there's no cure, and that I'm unlikely ever to feel much better (only worse) it has certainly explained why life has been getting harder these last few years, and why I couldn't just "snap out of it", or "pull myself together".
Previously, I had an unknown enemy. Now, at least it has a name. I know I'm not going mad, and that I'm not lazy, or stupid, or any of the other things I was beginning to suspect.
I don't know if I ever want to accept it completely. I accept it in the sense that I no longer torment myself with: "Maybe it was a mistake?", "Maybe I don't really have it?" I'm satisfied the diagnosis was sound, and that I needn't search for alternative explanations. Though in my case, some of the alternatives were worse - so my neuro did a good job of persuading me MS wasn't the worst outcome. It was unlikely to kill me, at least - some of the others might have.
I suppose it depends what you mean by "accept". Accept it as truth? Yes. There's no point trying to deny the bleedin' obvious.
Accept, as in not fight? No, I think I shall always fight. I haven't chosen to do it with DMDs (a purely personal choice), but that doesn't mean I feel there's nothing I can do. I've lost a lot of weight, and I probably work much harder at fitness than I did before I got ill.
I know these can't halt or reverse MS, but I do think they'll put me in a stronger position to deal with whatever comes.
When I get a bit down, it sometimes helps to remind myself I've had it ages. Although the diagnosis is newish, the illness isn't - I'm sure I've been "managing" it for years. I'm not a different person because somebody slapped a name on it. ;)