Which ex gave me herpes?

So I'm still waiting for lab results, but I'm pretty positive I have herpes. I noticed symptoms after having unprotected sex with my ex boyfriend. I hadn't had sex with anyone for a year, that person was female(can women pass it to one another?) and to my knowledge the only other person that my ex bf has been with is his ex girlfriend who he just broke up with.

How soon after you contract herpes do you have your first breakout? How do I know who gave it to me?

If my tests do come back positive, do I have an obligation to tell him?