How do I know if the grass isn't greener?

I was single for about two years after getting divorced until I met someone. I've now been in a new relationship for almost six months, but I have this feeling like I missed out on meeting people and didn't stay single long enough.

This wouldn't be an issue if the person I met wasn't a great match, but they are. They treat me great, we have fun and share common interest, and I still have a strong attraction to them. My problem is the "grass is greener" effect. After getting hurt in my marriage, I feel like I should never settle. Like I can always do better, even though I know I have someone special.

I work in an environment where I meet a lot of people, so I can't avoid interacting with people of the opposite sex all together. I know this has to do with my failed marriage, because I never had issues with fidelity before. So, my question is how do I get past this and appreciate who I have before me and not gravitate to the attention from others, which could lead to cheating?