Sorry to read of your difficulties with Alec. My perspective: From your writing over the years you've made a conscious effort to give Alec no more and no less than any other partner, as its your way of handling all relationships. It seems like it's finally caught up for him, and perhaps he's ready for someone who can provide more than you're capable of. If so, that's probably good for both of you in the long run. No point in continuing a relationship where a partner is left with a mostly empty cup for the rest of their life. Too much of a burden for both, and not a very joyful commitment. Hopefully he's ready to let go and move on, and find a partner that will connect with him in a way that brings happiness to that part of his life.
Best of luck.