Tá buachaill aige
He has a boyfriend. / Tá buachaill aige.
(The discussion is empty, but it has the red message saying they do not want people to use the discussion. So I am posting here.)
What would "He has a boy" be?
gasúr is more used in the sense of a young child (Connacht) or a young boy (Munster, Irish). So there is some overlap, but not much.
However, you are correct. It takes context. Also, OP, these types of questions are fine for the discussion. Duolingo really doesn't care if you post there, as long as it's not spam. Asking serious questions is great!