Sky, I can read how much you are hurting and want this to work out. Listen to what you husband is telling you - he doesn't like himself. Thoughts of suicide, he doesn't think he deserves you (has he forgiven himself for the A?), he has left his hobbies behind, he is living with his Mom.... Don't pressure him at all. Don't try to reason with him, he is letting his emotions run his life - so validate how he feels.
Take care of yourself. Manage your energy. Get a support network, you have pets? Do things for other people. Make a list of what you are grateful for. Read the Serenity prayer.
What is your realtionship with your MIL like?
You can handle it.
Cheers
M22,H45,W45 S21/18D12 Retain faith that you will prevail in the end, regardless of the difficulties and at the same time confront the most brutal facts of your current reality, whatever they might be.