Yes, it can take months for the stress to reach a point where Midnight self-mutilates. The other cat sounds pushy though not in an aggressive way and I would suspect, having watched behavior interactions and long-term consequences for decades, that this has bothered Midnight for some time. You know how it can happen in a work place. You get a new person who is a bit annoying but you cope, then the coping becomes annoying, and then you get really frustrated from having to adapt. From your description, he is a needy cat who regards you as his own so this nagging annoyance has reached stress levels.

If you want to keep both cats, you might want to use Fluoxitine or similar. However, as moosmom has said, any tranquilizer can have multiple effects.

Can you give Midnight his own feeding area? Sam is bothered by the others (she has CRF so senses she is weaker than other cats) and has feeding bowls on a table in the bedroom. It's easier for her to smack the others down from the table than cope with feeding alongside several other cats on the floor.

There are pet behavior therapists who can help.