one of his "I ought not to have companions because they suffer too much" phases.

Which is utter nonsense on the part of the screenwriters. Becoming a companion does not mean that you're doomed. Most have gone back to their old lives; some started new lives elsewhere. Almost all have become awe-inspiring people as the result of their time with the Doctor. Only a very few have died, and those were more in the "ultimate sacrifice" vein than anything.

I don't know why something that does not exist--the motif of the Doomed Companion--is becoming a theme.