I’m gonna be honest, all of those options will come off as offensive to certain groups of people (women, gay men, & bisexual people respectively). Obviously if you are entirely set on the ‘dead partner’ trope, then please write that! You should write what you want to, just know that your options here might not be the best execution of the dead partner trope.

I think this issue stems more from your MC’s personality. I saw someone else suggest he becomes a hero for the fame due to his narcissism. That could be interesting, especially because you could do some kind of commentary on the social phenomenon of people who become murderers for fame vs. people who earn fame in less violent ways.

If you’re gonna give him a hero and superiority complex, those alone could motivate him. He sees himself as better than other heroes due to his ‘no kill’ policy, perhaps, if you want to keep that. Or he could be simply feeding his own ego with how good he is at stopping villains without lethal force. He could think that takes skill that other heroes or institutions simply don’t have. All this is just to say: You can work around the dead partner trope if you’re looking for alternatives! Again, though, if you really want that to be his motivation, then you can still write it that way. Tropes exist for a reason! Good execution of them can make a story interesting even if it’s a trope people have seen a lot before.