Night crawling is BAD!?

The leading character is a virgin, reserved, "otaku". His work is home security. By strange accident, his father remarried and he got a new family.

...My sister-in-law looks at me really coldly. However, I am panting and suffering with mental anguish over the sister-in-law in my new family.

I couldn't stand it anymore so I decided to do night-crawling. If I am found out she will look at me even more harshly, and treat me as sheer waste. I need to have sex with her without being found out.