Would you tell your bf when a past FWB texts you?

A few weeks ago, my bf traveled to a different country and we’re now doing the whole long distance thing. Within 15 mins of saying bye to him at the airport, my past FWB texted me (whom I’ve not spoken to since I got into my current relationship). He just sent a memory that came up and we texted for like 3 mins and it was over.

I didn’t mention it to my bf.

4 days ago he texted me again, but this time there was more of a conversation. He kept asking questions and I’d answer and not ask him anything back.

Again, I didn’t mention it to my bf.

Today my bf and I got to talking and he started asking about my past and then we got into when ex’s text and he asked if any of my ex’s texted me. I told him about my past FWB. He was understandably upset. I feel really bad and now I feel like I should’ve told him earlier.

I keep asking myself why I didn’t tell him before and I guess it’s because I wouldn’t call him an “ex” since we were never in a relationship. The conversation was also just friendly. But still, I know it was wrong and should’ve told him.