Itsu made mo Musuko no Mama ja Irarenai! (いつまでも息子のままじゃいられない！)

The protagonist, Subaru, has been in love with his mother for a long time.
While trying to hide these deplorable feelings, one day, he accidently pushes her down.

However, she agrees to be his lover until he gets a girlfriend.
And so, the journey trying to become a real lover with his mother begins.