I imagine Johnny to be the kind of guy to fall for a girl who also has powers, like hear me out his whole thing is that no one has ever been able to keep up with him, not physically, more mentally. Also he's always looking for someone who intrests him.
Now picture this, the fantastic four have just managed to end up on earth-616, reader, has just broken up with her situationship, if you can even call it that. She's got powers, for the sake of the plot (opposites attract) water powers, basically like Johnny's with a hint of percy Jackson, can control water but can also transform into water, if you get what i'm saying.
She also feels like Johnny, not many can keep up with her mentality, so when Johnny comes along, with his charm and wit she's convinced she won't fall for it, until she does.
In the little things he does, like when he watches her train with that awe look in his eye, the moment she catches him he puts on that charming smile, or the way he always has a spare bottle of water for her.
He gets flowers sent to her desk, not roses, never roses, that's too basic for Johnny. He'll get some exotic flower that's only found in the wild until he can find out what your favourite are, but for now he'll settle for some never been seen before flower in your favourite colour.
Johnny's used to dramatics, mostly people not handling his dramatics, so when you match him on that front, he's quite shocked. The way you fly with him in the sky, he might aswell have proposed then and there with how in love he looked.
Anyway, that's my take on being Johnny's lover. I just think it would be full of dramatics but also shared quiet moments.
