When I found out I had stage III cancer, told my H via phone after phone call confirming the cancer. Told my two kids face to face individually but told them things were going to be OK, that I was going to be fine. Sounds like best for you to talk to them individually, telling them once you decide something final if you decide you will be getting divorced. Individually you can hear their concerns and answer any questions.
What makes your situation painful is that his behavior is his choice.
Sorry you are facing this current situation, and all the best as you sort through to a better future.
We waited 4 months to tell our two together in person because we wanted them to know at the same time and to hear it from both of us. I didn’t want to have to decide which one I told first. We changed our minds several times about the when and how. It was not a shock to them. Both were in college. Honestly, I think what they needed to hear most was how it was going to effect them. Months later when I had a chance to move out of state I talked with them about how it would affect them as well. Best of luck to you. I’m at the end of the process and hope to have it finalized by end of the month. I hope you have a strong network of support. Best wishes to you.