Renai Shiki ga Tokenai Sono Wake

Gyoshin, a 35-year-old gay man, has to go back to the countryside for some reason. One day, at a bar, a cool, good-looking guy named Sasho hits on him and pushes him down, only to find out that he's a high school student 17 years younger than him! He lets him go home without doing anything, but the next day he runs into him again at the cram school where he works, and finds out that he is the son of the man who was his first love! Gyoshin has been keeping his distance from Sashin, saying he's not in love with him, but when he earnestly confesses over and over again that he's always loved him, he's gradually moved by his feelings and...... Source : Pixiv