I know this is a plot of a lot of yaoi mangas lol. I believe the art has a sketchy rough feel. They are childhood friends, the seme gets made fun of because he is really tall and the uniform looks funny on him. The seme has sex with a older women when he is young. The seme is light haired and the uke is dark haired. The seme rapes the uke in a playground/park area while it's raining. Afterwords, the seme gives him a towel/his shirt to clean up with. They go a couple years without speaking to each other but then talk again in highschool.

Moved to Yaoi/Yuri.

I think it's Awakening Puberty

That's it, thank you so much!