I know of a lot of people who have migranes who seem to get hypersensitive to pain in general.It's not a purely psychosomatic problem, it just means that overuse sets the nerves into a sort of short circuit where the mechanisms that dampen pain get bypassed. the same thing can happen with depression, which is why a lot of people get put on antidepressants when they have chronic pain.
That said, there are things he can do to better manage his pain, and these are relaxation excercises, CBT therapy to work through the anxiety, also mindfulness, a type of mental discipline, is very effective with this. These will not cure his pain, but they will help reduce the anxiety and the other psychological factors that keep him where he is. He needs to be reminded that closeness and intimacy do not mean losing himself in the other person or being "taken over" by the other. THAT will take a lot of time and work on everyone's part and is better takn on by a professional.
Good luck, but for your own self; You can only help him, you are not RESPONSIBLE for him getting together. That is up to him. The best love you can show him is respecting your own boundries and his. This is not something you are going to solve in a few good talks.
Best to start with the position that his pain is REAL, probably caused by central nervous system sensitisation by his migranes, bu that the other problems are making it hard for him to handle it.
And, make sure he has a thorough physical work up. He will take you more seriously if he thinks you are taking him seriously. HUggsss, and the best of luck!