Hi David, perhaps you are a victim of your own success: you have kept the father-son bond well, so he doesn't want that security threatened.
It is natural and normal for him to feel wobbily about you seeing somebody. Also, our children can often harbour hopes that we will reunite - no matter how unrealistic - if we are not seeing anyone else. If you have been 'single' for a long time this aspect might also bother him.
You obviously want to be sensitive to him. so you need to consider how much your 'dating' is directly affecting him, or likely to impact in the future. If he is expected to accommodate a new person right from the get-go, if you cancel times with him to be with them, if you compromise what he expects as 1:1 time early on, then tbh, it isn't a case of him being 'hard on you', rather you not realising how hard it is for him.
'Dating' implies a fairly casual beginning - it might be better to keep any new relationship to yourself until you feel it is significant enough to warrant an introduction. If things are casual, ask yourself how fair it is to bring people in and out of his life to suit your own convenience.
It is tricky, but at ten he is very young and his time with you must be precious to him. If you can put him first in the early stages of any relationship that will help him adjust and anyone worth their salt to you should understand that you need to do this.