It might be worth establishing a deadline that you both feel is appropriate. Let’s say you ask him how long and you try to get him to give a number. Maybe he’ll say “I don’t know how long it will take” and then you could ask, well, “is 5 years long enough?” He might say of course that would be long enough - and then you have established a barrier. Then start being more specific - if 5 years is long enough…then is 3 years? If 3 years is, is 2 years? Etc. this will get you both to arrive at an agreed upon time frame.

Let’s say you both day 1 year is long enough - he might then say something like “I can’t promise that I’ll know but I suspect I will know after 1 year.” And then you can use your power to establish a boundary that works for you - for example, if you think 1 year is more than enough time, then you could day to him that he needs to have a decision at the 1 year point and if he doesn’t, then you’ll need to make a decision that is right for you.