You are indeed being very logical in your writing.

There is a radical logical solution to your problem - commit to only deal with real problems in the order in which they arrive. In other words, if, at any point, your partner finds somebody else, you will then (but not now) deal with whatever feelings and issues will manifest themselves then.

But not earlier.

This is a great way because it is the most efficient - you will not waste time and mental energy dealing with non-existent problems. You will only deal with actual problems as (if) they arise, and if they do not arise, then you will have saved yourself a lot of mental anguish.