How exactly do Johnny and Sebastian connect?

I don't know if you're British but we have a saying "wet behind the ears" which means naive. When Johnny says "I'm still wet" it's the only time in the film he lays bare who he is. Someone who doesn't know as much as he thinks and still has a lot to learn about life. When he says "why me, why not my brother" he's reliving his dad physically assaulting him as a kid. He was the one who always got it. There's no actual connection between Johnny and Jeremy other than a possible metaphorical one.

Jeremy is Satan. Pure evil with no redeeming value while Johnny is like a fallen Christ. Notice the clock behind his head to represent an halo. That wasn't an accident. Mike Leigh wanted that shot in there. There's a hint of some humanity in Johnny somewhere but we see very little of it. In the closing shot, he literally doesn't choose a path. He walks right down the middle of the road. He might end up on one path and ultimately change or he might go down the same path as Jeremy who is beyond hope. But for now or possibly forever, Johnny is in between redemption and destruction.

I think Jeremy is also there as a device for Mike Leigh to show different sides of the same coin on a social level, and to hold a mirror up to the audience in terms of manipulation of cinema and storytelling. Leigh seems to be saying men can be sexist and abusive whether they are poor like Johnny or wealthy like Jeremy. Ultimately, there's not much difference between the two, we just subconsciously think there is because we mostly follow Johnny but he shouldn't nescessarily be given a "get out of jail free" card from the audience just because of his background and because he has most of the screen time.