Look at Heinrich taking all those young people under his wing. Look at him giving asylum to the emigrants. Look at him banging his head against FW2 and FW3, apparently incapable of giving up until the last year or two. Look at him being unable to give up command during the Seven Years' War, despite kind of wanting to. Look at him taking responsibility for the treatment of civilians in whatever region he had an army in. This guy was a problem solver, and you could argue that Mara, Kalckreuth, and Kaphengst, and the relationships therewith, were in some ways all problems that needed solving, in Heinrich's mind. The harder the problem, the more his inner terrier kicked in.

I suspect the sex was also fantastic, but I don't think that's the whole story.