Good friends gf found out about our past.

So I was randomly unfriended on Fb by a very good friend & his gf recently. I asked him what the problem was because I know I didn't do anything wrong. Eventually he replied & informed me that his gf found out about our past & lost her shit. We had sex with each other once nearly a decade ago. 
They just had a baby last month & I am Married & have 2 kids. My husband has known about our past for years. 
Am I wrong for being upset about this? Like I'm so upset I could cry because I'm afraid she expects him to suddenly stop talking to me & being my friend. I've known this guy since grade school. (20 years) 
Would it be okay to msg her & let her know that I am in no possible way a threat to their relationship? She knows that I'm married with 2 kids. I've been nothing but nice & excited for the two of them & their little family.