I can't believe you continued to sleep with this man after he gave you an STD let alone never using protection! Why would you even put yourself at risk?
I know what it feels like being in this situation, it only happened the once because I couldn't allow myself to continue despite the biggest intense connection me and him had, we still speak occasionally as we were really close friends but it's very rare as I don't want to be sucked in and despite how I felt about him I couldn't go through it again. So I understand how you feel, I get it but you really need to move on from this.
From what you write actually angers me in some ways as I developed something very strong for my old friend but at the end of the day it was never going to work out and I will never allow myself to play second best, I couldn't live with the guilt the first time.
You've said, you'll never be together, not that you should want a relationship with him, and considering he tells you you're "special" you feel anything but afterwards.
In future, no contact,don't answer the door or if you do slam it back in his face.
It scares me that you could potentially be pregnant, then what do you do?!
Get yourself checked out !
He'll keep coming back for a quick shag purely because he knows he can and you always let him! Have some self respect for yourself, neither of you are respecting you!