"I do not know how to properly justify going to bdsm sites and not having sex to him, because to him it looks like I'm searching for porn."

If its his house and his computer (or even his internet connection), I suppose he has the right to request that you not visit sites he doesn't approve of.

Demanding sex when you've said no is probably some form of sexual harassment, but if you need his place to stay at and you've been intimate in the past, I'm not sure what your options are other than force of personality.