Be honest and brave and communicate directly. Be clear with yourself how you would react if they were interested in getting back together and whether you would want to be “just friends”. Then… ask them what their intentions are This is a hard conversation to have, but it could save you (both) a long period of frustration and possibly unfounded hopes (on one side or the other.)
It would be nice if the heart were so unambiguous. Sometimes it does take some conversations to get clarity in order to move on.