I think you have been given great advice but I do have a soapbox issue:
You should NOT sleep with someone who is sleeping with someone else.
The moment I found about my ex's affair partner (who was married too) I went to the Dr. and he did too at my insistence.
I was negative, he was positive.
Please make sure you understand your life time commitment to your body and health.
I am sorry you are in this situation but STD's are no joke and someone exposing you to them without your knowledge is sh*tty!
M:47 M:18 D16, S19 1st S 1/08-5/08 Reconciled/May 7, 2008 Left again Nov 9, 2009 I Filed: Nov 17, 2009 Final: April 14, 2010 EX walked away from kids too