Little bro has MD and I need help

My little brother was diagnosed with duchennes 12 years ago. I am 8 years older and my parents are expecting me to take care of him when age catches up with them. My boyfriend and I have been talking about getting married. One of my parents' major concerns is the fact that they don't think that my boyfriend and I can comprehend the type of strain that my little brother would put on us, financially and stress-wise. I do understand that. I've seen that in my parents' marriage. They also think that we will not be able to support him financially. My boyfriend is a cop and is planning on getting his law degree, eventually. I am in school for business and plan on taking over the family business.

After ranting, my question is: am I really not understanding how hard it is to take care of a boy/man with DMD? and Should that dictate who I marry?