A question vmain
How old is your brother
Have you considered this? As a carer dont forget that Mental welliness is a part of life even when suffering a MI. Its not a life sentence & it can be a shock to the owner. Excessive thinking & worry does not help you support your brother, this will war you out. Having positive thoughts & keeping your norms in check is vital. Having jun is allowed & highly recommended.
It can becoming consuming in many ways, especially if you take on bros pain & loss. Grieving may have not been possible when you expected it.
I feel that shifting focus on your role might help. How long since you guys had a "normal" day out. Allow yourself to have fun & good times with your brother & mum. We play Yatzee etc & cheat & tell jokes & laugh. Watch Shallow Hal its must make you smile. Filling the glass with other things not related to MI gives less room for it. Feeling normal is doing normal things. Grieving for dads doesnt go away. It just changes. I miss my dad too.
Your best is being a happy you, you are allowed to be and genuine happiness is contageous & keeps the black dog away.
All the best