The thing with asthma is this. From personal experience and husband experience. Dependent on how bad it is, but at first probably always, you need to take medication every day because you need to get the inflammation, etc. under control. This will take a while and you have to be diligent about it. You also have to realize what your triggers are, i.e. if it is exercise induced only, do you have other triggers like allergies, is it worse different times of the year due to allergies. If it is mostly exercise induced and you go to high altitude when you are not used to it, it will be worse! Take your inhaler.
As far as the issues with your hubby wanting to do something and you do not, you have to decide what you want. You will probably never keep up with him. I was never able to keep up with my hubby, so we rarely road mtn bikes together, but sometimes road and I would draft off him a lot. If we got a hill and he left me, so be it! You have to realize that he has different goals and different abilities as a guy and not get weirded out about it. If you go for a ride with a group and get dropped - oh well. We all have our limitations. It is up to you do decide to like how, what and why you ride. Once you make this decision, everything else will be okay.
Go on rides by yourself at your ability level. Enjoy those. Go on rides with others that are faster and if you get dropped chalk it up to training!
If he wants to do the death ride and you are not up to it all but you still want to go, which as we all know is really difficult, just do 2 or three passes, go find a nice place to rest and watch the riders go by. Read a book, whatever. Enjoy the day the way you want to enjoy it!
I know it is hard to balance all this cause I had a competitive racer husband, but you just have to decide what you want and then live within those boundaries. This does not mean that you don't try to get better, but you do it at your pace, not your hubby's.

