[Inahosha] Rokugatsu no Ame

This isn't NTR but it gives off the vibe. Those two are his childhood friends who told him his sister was dating an old man. he goes to see and ask what she's doing but it was actually his dad and he saw them going to a love hotel. Blonde guy had a hunch it was his dad but after seeing him he remembers it was def was. He seems shocked and doesn't know how to feel so he just standing there and his friends come and girl cries feeling bad for him. I think he's pretending he never saw his sister but then says they should have fun since they're at her favorite love hotel and walks away friends looking down.