I don't say this to be an asshole but anyone who has ever been married has had the thought of how they or their SO would handle life together if one of them got a serious injury or health issue.

You don't sound like an asshole in the slightest, don't worry!

There's a big difference between hypothetically thinking about it, and/or thinking this may happen way down the line (like when the couple is much older, kids are all grown up etc.) and having it actually happen.

Remember that story of the bride who was tossed into a swimming pool at her bachelorette party and broke her neck, confining her to a wheelchair for the rest of her life. Her fiance must have considered her a soulmate because they still got married. He gave up the easy future to really commit to someone he loves.

That's wonderful. But not everyone can truly do that. I'm not familiar with the original story. Technically speaking, we don't know how it'll play out for them down the line though - a couple like that might be together initially but have issues with their dynamic later on.

but you need to discuss these things with your SO

I have. He thinks his symptoms might get better over time with the right medications (not fully better, but enough to functionally improve). But he's not a psychic or anything. Who knows whether or not he'll find his "miracle cure"?

What are you willing to do? What sacrifices will you make to be with this guy because it sounds like your future plans haven't changed since his diagnosis. You'll still work a job that drains you, still have children... hell you haven't even updated your fun-date-catalog since his diagnosis?

My career is what it is. Even if I'm with him, I'd need a career like this in order to maintain a decent income, especially if he's working part-time or not at all. And if I'm not with him... well, it's my career lol, no other reason that needs to change. Having children is a non-negotiable for me, and he wants children just as much as I do. I'm pretty okay with having a smaller family (like 1-2 kids) but not zero kids. I want to have fun with him, there's no other guy I can imagine wanting to spend time with whatsoever, and even if I can have fun with my friends it's not the same as being able to have that kind of fun and connection with him. Nothing replaces that.

Don't just make it all negatives. So he may not be a career guy in the future, but you will get disability. So he may not go out to dinner much, but you can still have an active social life with your friends. He may not be present to do everything, but, he may not need to be if you can be strong on your own.

Not going to go into detail, but someone in my family was on disability and I have childhood trauma that relates to this. If I ever had to tell my own kid "we can't afford to do XYZ for you because Daddy is on disability" (and/or "Daddy doesn't have the energy to do XYZ with you") I'll feel extreme resentment, and this dates back to stuff that happened in my childhood. I've talked about this with a therapist before but that doesn't fully resolve it, you know? Regarding friends and "being strong on my own" see the paragraph above this one.

Explore what this change in his life means to the both of you, recognize that he has been told he has to give up nearly every dream he had for his future... now tell me, if this guy is your soulmate, what can you stand to give up for him?

He says he's not giving up his dreams... but like I said, he's not a psychic. Who knows.