 If you liked
Niichan
|
 ...then you might like
Josou Danshi to Menhera Ojisan
|
Without revealing too much, I'd say that these two manga are very, very similar. You have an older man who shows sexual interest in a young boy, a boy whose entire life changes after he meets said man, a realistic/likeable female friend and confidante of said boy (very rare in BL manga) and the emotional struggles of the boy as he comes to term with his own desires and sexuality.