For my marriage, the hardest part has been acknowledging that the AVM doesn't only affect me. Sure, it affects me more, but it's not all about me. I didn't realize this until my husband broke down crying one night because he "couldn't bear to lose" me.
Since then, it's been a daily struggle. Dealing with an AVM is hard enough. Dealing with an illness like this while trying to nurture the most important relationship of your life feels impossible at times.
Every day is a new challenge. David (my husband) oftentimes seems to just want his old wife back. That hurts, but I'd be lying if I said I'd feel differently in his shoes. I was diagnosed just two years after we got married, so we didn't have decades of marriage to fall back on. It's just so hard to watch our relationship change and know it might never be the way it was.
I think we should expect these things to affect our relationships. They're going to. Like someone else said, tragedy is either going to make relationships stronger or make them weaker. Some people grow closer in the midst of crisis and some don't. In the end, I hope you and your spouse do what's best for your situation.