I suppose it all depends on how much you want this relationship to work out.
I can only base my answers on my own experience.
My balance was the first big shocker. I looked drunk all the time. I was drunk quite a bit of the time. (well if people re going to talk about me, give them something to talk about).
He will need time to move about safely. What you can do is show patience and let him take his time.
With good support from his MS team and the right medication there is no need to assume that he will go downhill any time soon.
To be honest, the best thing you can do for him is to be a sort of invisible support. A good friend of mine just holds my elbow if I start to wobble. That is the perfect way to stop me wobbling. Not an obvious arms around me. just a subtle guidance.
As for how his MS will progress, it could well remain stable, he could have the occasional times when he feels/appears worse but that is par for the course.
We have good days when nothing can stop us and bad days when everything goes to shit.
That is a human thing not exclusively an MS thing.
What I often need is a break from the treadmill that MS has me on.
A good day/weekend which can be looked forward to and which gives me a lift when I remember it.
The best times that I had were when a friend who works for Network Rail gave us Oyster cards and Tickets to London.
It was only a weekend but we walked over the millenium bridge to the South Bank, went into the Tate Modern which we both enjoyed and dragged ourselves away after 3 hours only because we needed lunch (me) and beer (husband).
The bars along the embankment were fab.
Another event was going to see Roger Waters at the Manchester Arena. He can get a free ticket for a carer, which means that you can both go for the price of one. Is your fella aware of these carers tickets? they need to be applied for when booking tickets.
The thing that is important for me is that I need to feel safe in the venue. The Arena makes me feel dizzy as soon as I go in. So I bought tickets for a box. Those VIP boxes are fantastic. You have a small room with a balcony. In the room there is a bar, unattended but with a telephone. I picked up the phone and a voice asked me if there was something I would like, I said that we would like a drink and the next thing was a waiter appeared with our drinks. That was excellent as queueing for drinks takes ages and is like a mad scramble.
So try suggesting going to a gig. As a new relationship the bond of liking the same music should not be underestimated.
Think of it as a glass half full, not half empty.
I hope my reply has been useful.
Wishing you both well.