Basic Trope: The Mole starts to like the surroundings he's infiltrated.
Straight: Melvin infiltrates the Five-Man Band and pretends to join them. During his time with them, he starts to legitimately enjoy their company and the way they do things.
Exaggerated: Melvin pretends to join the Five-Man Band and immediately starts enjoying their company.
Downplayed: Melvin infiltrates the Five-Man Band to betray them, but decides they don't deserve it and just leaves instead.
Melvin really didn't like his life beforehand. The good guys show him that life is worth living.
Alternately, Melvin genuinely wanted to join the good guys to begin with, and his job as The Mole was just an excuse to get out from under his evil employers.
Inverted: Melvin questions himself and is on the verge of doing a Heel-Face Turn, but after infiltrating the Five-Man Band and hating them he realises that he was right all along and becomes much more comfortable with his betrayal.
Subverted: Melvin didn't really start to enjoy things...his act was so complete that he was even able to fake a growing sense of camaraderie with his victims.
Double Subverted: At least, that's the excuse he gives when he has to go through with his betrayal...
Parodied: The Five-Man Band makes Melvin do all their laundry and cleaning, and treat him with barely-disguised contempt, he still insists he loves it.
Zig Zagged: There are certain aspects of that life Melvin missed, but overall, he doesn't seem too broken up about it.