I think learning to drive will be great, don't know about the licences though, sorry.
How has your DP reacted to you learning to drive?
He does sound as they he may be depressed, but it's very unfair on you that he doesn't seem to be taking steps to address his MH issues. The reaction to the tablets sounds terrifying, but I do know thoughts like that can be a side effect. I have to take (I think this is the right word) trycyclic anti depressants, they are actually for nerve pain but have helped my insomnia immensely, which has had a huge beneficial effect on my MH - but this may be the improved sleep.
From your posts, what stands out to me is that his behaviour is very selfish - would you say he is a selfish person generally? I think with chronic pain it's so easy to become self centred as you are focusing on yourself a lot, I do find it's an effort to remember other people but with my family and particularly DH (as he does so much) I try and keep their well being at front of my mind too.
If he isn't making any effort to think about your well being, well, it would make me question separating, very honestly. Your partner should be the one who always has your back and does try to support you, to their best of the ability. It's the effort isn't it, can he put the effort in?