Scared to upset my boyfriend

I am in a wonderful relationship with my boyfriend. We just moved in together, we plan to get married and move closer to his family and we’re managing the stresses of quarantine beautifully.

I have an ex boyfriend who I still love and feel connected to deeply. Based on a lot of past circumstances my boyfriend and I agreed I would cut him out and stop talking to him. Last Thanksgiving my ex texted me a quick greeting and I greeted him back. This caused my boyfriend to be very upset because “We agreed. ” And “No Contact means No Contact”

I understood and after we made up I admitted that a part of me still hopes that one day my ex and I can be friends again. But my boyfriend doesn’t see it as plausible any time soon.

My thoughts about my ex have increased during the pandemic. I really want to reach out to check on him and see if he’s okay. I want to ask my boyfriend if he would mind but because this is such a hot topic issue. (Really our only area of real conflict) I am scared that just asking him will upset him. I am scared that he will make my question mean something about us or him. A part of me knows we need to be able to talk about anything if we’re to be married one day but this one issue seems too loaded to bring up.

I am considering doing it behind his back but I don’t want to lie just because I am scared.
I want to feel calm when I ask him, not scared. How can I get there?