I think the best way to make the character suffer is to ensure all the things that go wrong are a direct result of each of their actions to try to make things better.
So he tells his lover he's going to run away, hoping she'll go with him, but she goes ballistic and breaks up with him. He goes to his best friend to ask for help sorting things out with the girl, but his best friend gets angry at him for asking and also stops talking to him. In an attempt to make a grand gesture to his best friend, he gets in trouble with the police. While on the run from the police he trips over a nuclear reactor and... well, you get the idea.
I think you need to go back to basics and make sure you have a solid starting point for your plot, because at the moment it sounds like you only have a kernel.
I would recommend starting by considering the five major plot elements:
I'm going to complete these for you to show you what I'm talking about, but you should replace all of this with your own ideas:
- Character - the boy. Let's call him Felix, for no particular reason
- Situation - living in a world of constant rejection
- Objective - find a place where he feels supported
- Opponent - A violent stepfather (for example)
- Disaster - He risks losing his newly found passion, his best friend, his lover
So, your premise would be: Felix has decided it's time to run away from a life lived with constant rejection. But even if he can overcome his violent stepfather, he may discover that fleeing will force him to lose the only things in his life that really matter.
Once you start looking at those you can start to see some gaps (such as an opponent) in what you've described above which in my opinion you need to resolve before anything else.
Here are a few of the questions that it raised for me:
Why is he planning to run away? Usually running away is a very spur of the moment thing, not something you sit down and make lists about.
If he discovers all the reasons he should stay while writing this plan, it sounds a bit like a non story, as the thing he wants to do, he never actually does.
Are you saying he realises all the things that are important to him and then they get ripped away? I'm unclear on the order of events here.
So, in general, I think you've got a lot more work to do on getting a decent story structure, and if you do that, then you will naturally find out how to make your character suffer.
I would especially suggest using the technique of 'Goal >> Conflict >> Disaster' in order to achieve an effect where things are constantly getting worse for the character.
You can read more about that here: https://www.novel-software.com/roadmapstep6
(disclosure - that is my website)
Sorry if it's not a very concise answer.