abuser M1G... oh your mind. you should tell us more of these wonderful thoughts
you should tell us more about how he treats Legs
it probably starts with small things, especially before M1G regains some of his memories. little acts of physical violence you could pass off as just friends messing around, and of course Legs kinda just reciprocates that because he assumes that's just the kind of friend M1G is. M1G then takes this as a go-ahead to escalate (especially since Legs HAS been known to straight up whack M1G over the head when he "spaces out" lmao). because of course it's normal to drag someone by their hair when they won't follow you or grip their arm so hard it bruises to make them focus. that's just how you get what you want! (and Legs doesn't do much about it other than an "ow, okay, I'm sorry, stop that" because anything more could lead to a disagreement.)
as they get closer and more comfortable with each other it gets worse. Legs gets used to M1G's behaviour and stops reacting the way M1G expects, so he has to push it further. to the point where he'll just choke Legs until there are tears in his eyes if he makes a mean joke on the wrong day, or straight up slap him to stop him talking. Legs ignores that this is even happening whenever possible, he just doesn't think about it too hard.
on the flipside, as they get more "comfortable" around each other, M1G gets more affectionate. and that's based on how things are within the Collective, which is pretty different from your standard relationship... he has no idea what consent is. his way of showing love is just sexual harassment. a hand up his shirt or squeezing his thigh whenever they're alone (and he doesn't stop when Legs pushes his hand away, because why would he? he's just expressing his love). if they accomplish something together (like finishing a building) he'll pull Legs into a kiss, and keep him there while he's trying to get away, until he stops fighting and reciprocates. Legs stops complaining pretty quickly after he realises he won't get anywhere without causing a scene. he knows M1G means well, so maybe if he forgets he has no say in it he can enjoy it. even when M1G climbs into his bed with him and starts feeling him up (I can see Legs joking that M1G is just like Mike. to distract himself). he can ignore how he's freaking out and scared of what M1G might do if he falls asleep.
I like to think the first time it goes beyond touching is the day of catmaidcon. M1G wasn't there for the actual event but he probably woke up later to Legs in a maid dress and took the opportunity. he was parading around flaunting his body, surely he was fine with M1G appreciating it. this ends up with Legs pinned against a wall, begging M1G to get off him but not physically fighting him. M1G is gentle, too. his affection is seperate from his violence, at least in his eyes. this isn't a punishment, it's a reward.