I was recently cut by a friend's razor blade that he had left behind in his room before he took an approximately 6 day trip. When I began to bleed, I rushed to the bathroom to rinse the cut, applied a paper towel to stop the bleeding, and then applied hand sanitizer several times to ensure it was clean. Afterwards, I examined the blade where it lied and noticed there was no signs of blood, dried or fresh. He informed that after each use, he rinses it and drys it with a towel. The problem is he has never undergone STD testing despite being sexually active; from what he told me, he has used protection in each encounter, but did without one in the past 6 months. Should I be concerned?

I would get tested just to be on the safe side. You did cut yourself with another person's razor, so I think you owe it to yourself to be screened.