I had a similar situation, and Facebook allows you to turn off your chat icon on your messenger app and this means the people who are online don’t show up constantly when I’m checking my inbox (turning off my active chat button really didn’t change how I used the app as I tend to just scroll down to whoever I want to speak to rather than finding someone on the active chat list, and I expect vice versa) This helped me as I no longer could see when he was online and it wouldn’t give me the intense anxiety over who he was speaking to. Also I’ve deleted my Facebook and Instagram apps at the moment because I spend way too much time on there anyway and this way I won’t be tempted to stalk!

Hope this helps ❤️