Wasn’t going to say anything, but our Poll’s sensible, so I’ve gotta say, I’ve got reservations too.
He is, in many ways “the love of your life”, as you put it, yet at no time has he confided openly to you he has MS, and you were left to guess, and then overhear him telling someone else?
Of course, it’s possible he didn’t tell you out of fear of losing you - it’s not an easy thing to come out with. But might there be a mismatch between how you see the relationship, and how he does? Is he, like you, thinking of a possible future together? If so, why hasn’t he felt it natural, or even a duty, to lay his cards on the table? Is it that he doesn’t feel you are close enough that he owes you any revelations or explanations about his health? He’s evidently told some people, but you weren’t in the circle he chose to tell. Why not? You say he was “the love of your life”, but was it reciprocal? Might you just be a face from the past who has cropped up again, but not anyone he’s ever thought of as “The One”? I know that doesn’t necessarily mean he couldn’t have his eyes opened to the possibilities, but it’s a bit of a concern if you’re already thinking LTR, whilst he’s not thinking of you as a privileged confidante he wants to share his thoughts and feelings with.
And then there’s why you are pushing the discussion, if he’s obviously reluctant. Isn’t it up to him how much he decides to tell, and when? I do understand your concerns about your future, and that of your little boy. But the one thing that would help you decide is the one thing your friend, or even his consultant, couldn’t tell you: how it’s going to go! So if you cannot learn anything helpful from the discussion, why are you so insistent it must be had, against his wishes? He can’t know his own prognosis; he can’t tell you what you might have to put up with in future. If he talks about MS at all, he can only tell you how he is now, or talk in general terms about things that may OR may not happen in future. He can’t offer you any certainties, because there aren’t any.
As for the whole diet thing, it doesn’t sound as if he’s had that on good medical authority. I don’t suppose a lot of processed foods and fizzy drinks are great for anybody, but there’s no evidence they’re a special NO for people with MS. A healthy diet would have the same benefits it would for anyone, but there’s no evidence it would do anything special for the MS. Smoking, on the other hand, is different. There’s mounting evidence it’s one of the few lifestyle choices that has any effect either on risk of MS, or disease progression. So it’s a change that’s really worth considering. BUT if someone is already struggling with their illness, and suffering a lot of stress, quitting smoking might be better as a long-term goal to aspire to, rather than something they should try immediately. You have to balance any health benefits with the stress of the attempt - which, if someone’s already not coping well, might be an unreasonable burden. Breaking old habits is hard at the best of times, but more so if someone is already having a tough time.
If you see your future together as reforming what he eats, and whether he’s allowed to smoke, I share Poll’s concerns. It would be different if he was actively enlisting your help to change things he’d like to change anyway. But if he’s happy eating ready meals and smoking, a mission to convert him could cause friction.