Is he the same friend from high school, or is this another twin thing?

Same friend

Same person, you can see it when he sees him again.

Ahh i was confused because of the picture in ch 6 page 8. So i guess black hair is ML and he was kissing his own brother(?) in the flashback (ch 2 page 23)

Yes. So the brother was light haired (I think he died?) and ml was originally the black haired one but he later dyed his hair blond when he became famous.