Fear or gut feeling in my relationship?

My boyfriend and I have been dating for about 4 years and we are discussing marriage. We get comments as well from everyone because of our age I assume (40 and 45 and people know I want children of my own). We went on a trip in April and had a great time and decided to go for it, so when we got back, I went and looked at rings and all this fear and nervousness started in my stomach and chest and I felt like I couldn’t do it, so put the idea on pause for now with him. I’ve done a number of models on this and done the Byron Katie work as well on a lot of my thoughts around him, our outstanding issues/differences, and marriage itself. They never seem to give me a way forward but just change my thoughts for a brief period.

I’m still left with a question and that is: How do I know if this feeling I get in my stomach/gut and chest is a gut feeling that this isn’t right/he’s not the guy for me or if it’s just fear? When is it intuition or a deeper knowing and when is it just fear of the unknown, etc?

Any thoughts would be appreciated.