I think it's a common fear a lot of people who have a MI has. I know, 3 1/2 years into mine, that I still feel like he'll betray me when I started to feel depressed. I agree with Bryan though, being open and asking questions helps a lot. It is a rough road to be in a relationship (MI or not!), but it ends up being the most worthwhile thing when you find a person that is kind, considerate, and loves you for everything that you are.

Having good communication is important! :') Don't be afraid to ask questions.