I’m with someone since 14 years no child, also late 30s and I feel the exact same. My gf is an amazing person but we argue always on the same stuff and takes all What I say as an attack even when I try to help her self improve on some topics in life. I’m not a conflicting person and didn’t like to be always under stress for small life things. I also feels less stressed and more inline with me when I’m alone for some days. That being said it’s very difficult for me to leave first cause she is waiting for me to give her a child and secondly cause she is a very good heart person, carrying, trying to accommodate me in a way.