Hikikomorimuke Hitozuma Sensei 

ひきこもり向け人妻せんせい

The protagonist's mother passed away half a year ago. He is a university student and currently live alone at an apartment. After her mother's  death, he decided not to go to university, so-called NEET -hikikomori-. He doesn't go out of his house and just play games all day. But one day, when he goes to the university for a change, he see a female teacher masturbating....