Naisho no Yorimichi

You (the protagonist) are a young man who works from home, and your two younger cousins often come to your house after school. They love you very much.

But summer's coming soon...your cousins, who have been busier with school activities--
"We might not be able to stop by much anymore...", they tell you with lonely faces. This is a very sad turn of events for you.

From then on, the twins come to your place less and less, but you're trying to enjoy your life nonetheless.
But one day...one of them comes to you with a confession of love. Although you were hesitant at first, their sincerity won you over. After that, the one that confessed starts visiting you again, keeping it a secret from everyone else...

[translated from Getchu]