However, he’s only really like it with me
It's natural to relax around people, which sometimes includes showing them an unpleasant side to ourselves. However, when it's taken to it's extreme, they do this because -
a) They don't think there will be any consequences to their actions (which is important, because empathy isn't enough of a reason for them to curb their behaviour)
and / or
b) You have lost some value to them that you used to have, which made it worth it for them to behave better.
I totally understand why you would characterise it as Jekyll & Hyde, because it looks like that and feels like that. However, I urge you to stop using that phrase, as it encourages you think of him as two separate people, rather than a whole person.
The person that someone is when everything is going their way, when everything is going well doesn't mean a huge amount. I mean, why would it? It's easy enough for a lot of people to be loving, generous, kind when their needs are met, isn't it? Unless they're some kind of sadist, they'll be quite happy that they're getting what they want and that will put them in at least a neural or good mood.
It's what they become when they DON'T get their own way that reveals who someone is as a whole person. THAT'S when you see what they're made of.
If they punish people over minor disagreements with hours of silence & moodyness, ruin days out, have a tantrum like a toddler because you haven't done exactly what they want you to (however unreasonable), or they punish you when you stick up for yourself, when you try to resists controlling behaviour.....then you don't really have a life partner that is actually on your side, only an opponent in waiting.