I read this manga some time ago but I forgot to add it to my list and now I don't remember the title. I hope it's not a figment of my imagination.

There was a young guy who lived (somewhere not in Japan, I think) with a lady (a friend? a family member? I don't know) and they were taking care of a boy who was a bit like a wild animal, didn't trust people and I think he didn't talk either. But after some time the boy started to trust the guy and they became friends.
But the guy had to leave the place where they lived (I'm not sure about this) and he had some kind of an accident and lost his memory and didn't remember the boy anymore. And after some time (a few years, maybe) the boy goes to live with the guy again (and now it's in Japan, I think).
I also remember that the guy was popular with girls and one of them was rude to the boy because he was stealing the guy's attention and she felt jealous or something.

I think the manga was shounen-ai, but again, I'm not sure.

Maybe Super Lovers ?

Yes, that's it!
Strange, I actually saw this manga when I was browsing through the "amnesia" category, but I thought it was not the one I was looking for because for some reason I was thinking it was a shounen-ai, not yaoi, and that it was not so popular... But now that you suggested it I checked again and it really is the title I was looking for.
Thank you very much 🙂