This possibly could have been a television movie and most likely shown on Channel 4, sometime between 2001 – 2004 (otherwise BBC or ITV1). It was English language and colour, however I can’t recall the aspect ratio or much else.
My only memories of the plot consist of a bullied teenage guy who is in a poor relationship with his father (possibly abused by him but I cannot remember exactly). I think he climbs out of a side window to escape the house on a regular basis so his father doesn’t know he’s going out.
Early on we see the interaction between the guy and local thugs who tease and bully him on a daily basis.
We are then introduced to a blond? girl who possibly saves him from the thugs or shooed them off etc.
I can’t remember anything between then and scenes where the guy shows the girl his secret hide/camp, that he has built and furnished.
Eventually interspersed between further scenes of the scraps/abuse between the guy and his father (shown only through windows from the outside of the house with audio) and the guy continually meeting the girl again, they inevitably fall in love and share their bodies with another on the ground within the hide/camp.
However the ending is not a happy one with increased tensions between the guy and his father. I seem to recall the guy possibly intending to murder his father which he declares to the girl, but it didn’t take place or something else happened. The last we see of the guy is when he climbs a tall brick wall fronting a railway line and we see him jump from the top of the wall into an apparent oncoming train.
The girl not knowing what has become of her lover, as routine waiting for him within the hide, visits the house and father (shown only through windows from the outside of the house with audio), where she first learns of the suicide and confides in the father. Then the movie/programme ended.
It is My Brother Tom (2001). Of course it was a FilmFour drama. Crappy handheld video and awful acting. I certainly must have not seen it all through as on reviewing now again it had a lot more going on… the girl confronting the father at the end about his sexual abuse of his son (which indeed was the arc), turned out not to be as I remembered. The whole thing about scenes only through a window was only one sequence. The jumping from the wall into train was a bridge. Anyhow I hate to have used it and say it but it was chatgpt that took my description and found it right away. 25 years have now been settled on this, can’t believe it. Whether a copy could have been seen online until more recently is another thing.
And how stupid of course now Ben Whishaw is totally recognisable supposedly 21 when he made this crap. The girl even went on to make some stuff to.. despite her voice and acting!

As suggested previously, it’s not Nature Boy (2000), although that has some similar plot arcs and otherwise an excellent miniseries itself.