tldr notes:

• he was imprisoned in the mirror forever ago and he served countless owners up until he was given to the evil queen. he served her faithfully until he was brought out of the story book, where—for the first time in forever—he had his human form again. he still has some of his powers from being the mirror, but he only uses them for nefarious deeds since he also has a slight fear of mirrors and his own reflection now.
• speaking of nefarious deeds, almost immediately after being brought out of the book, he was greeted by the cheshire cat who knew exactly what he was and took him under her paw. she brought out the best (and worst) in him and together they committed crimes, starting small with petty theft and then working their way up to the harder stuff.
• she was always in charge and the ring leader, and he liked that about her as much as he liked the thrill of being out of the mirror and getting away with the crimes he committed with her. the two quickly "fell in love" (who knows if it was actually mutual or not) and they were over time grew a name for themselves as the second bonnie and clyde, the new joker and harley. over time, though, this thrill and fun quickly turned into something akin to fear. and as much as he loves her, he was also scared of how easily crime and evil deeds were for her. part of him started to wonder if maybe he was just being used and if she'd ever do something to him if he ever said no to something she wanted.
• because he loves her, he thought it would be okay to bring up what would happen after they grew tired of crime, and she basically answered something along the lines of "who grows tired of crime? lol you're so funny" and that's when the fear really started to settle in. he didn't acknowledge it until he started having nightmares about being trapped in the mirror again. long story short, those were a reflection (see what i did there? hehehe) of his current situation of being trapped in a life he wasn't sure he wanted to lead.
• he eventually decided to face his fears and tell the cheshire cat "hey, i don't want to do this anymore" and ofc she's like "why? don't you love it?" and they get into a whole thing about it that ends up in him being gaslit and manipulated back into thinking this is what he wants. in the back of his mind though, he's still like "this isn't what i want" and it eats at him and eats at him.
• he tries to confront her about it again, but it ends up in a "you don't love us, you don't love me" conversation/argument but he stands firm this time. she agrees to try living a normal life with him but only to prove a point that he's going to fall back into their old habits. the two of them decide to settle down in fabletown together in order to do this, but she secretly still commits crimes while they do. he seems happier for now, but there is an itch in him that needs scratching... he just doesn't know what it is and for how long this happiness will last.