STD's

This is a hard topic to post about but I'm really scared about this. I'm worried that my XN might have given me an STD. I had no idea about his sex addiction until almost the end of our relationship which was before Christmas. As I ashamedly admitted before we were both married to other people and when we met we talked for about 5 months before we started a relationship . He seemed so honest and nice and not flirty or sexual at all, a little nerdy kinda. Neither of us had done anything like this befire( so he said with such honesty and endearment , blah!) so I didn't think of using anything, he did ask if he should for pregnancy reasons. Now, after reading about all these guys sex issues and cheating , etc,... I'm freaking out! I went to the Dr. The other day as I thought I had a bladder infection and it was negative.My friend said maybe I have an STD which never in a million years would I have thought of and now I can't stop thinking about it. Have any of you had this experience or worry? I know this is the right and safe place to come and get some helpful advice. I'm just so worried. Thanks for listening.