I overhead my now husband say something similar to a friend when we were dating. He said something along the lines of he didn't think I was the one. After his friend left, I had a very frank and honest conversation with him about our relationship. We didn't have any major ties together except for a lease on an apartment. I certainly didn't want to waste time with him if he didn't see marriage in our future. (Not near future but a strong possibility if things continued as they were.) I was very unemotional and talked through our options.

He was a bit shocked that I overheard him. I think he was even more shocked that I didn't want to play games and made it clear that I wanted to be with someone who would want to get married at some point. He slept on that conversation and decided that yes, he did see a future with me.

A few years later, we got married and are pretty happy now.

If you don't have kids, I would sit down and have a frank conversation about if you should stay married (ie should you even be wasting your time trying to work through this.) No one wants to be anyone's second choice, yet alone last choice.