Is the grass always greener on the other side when it comes to relationships?

Every time I look for advice, people say "the grass is always greener on the other side." We want what we don't have. Is that always true? I love my boyfriend who I've been with for several years, and we get along well, but we have very little in common and struggle to carry on conversations. Is... show more Every time I look for advice, people say "the grass is always greener on the other side." We want what we don't have. Is that always true? I love my boyfriend who I've been with for several years, and we get along well, but we have very little in common and struggle to carry on conversations. Is this normal in long term relationships? I love him and I think he is funny and smart and I care about him, but I find that my mind wanders to other people.

I have met a guy who I have so much in common with, and I like him a lot. They say "don't leave the one you love for the one you like," but what if the new relationship would work out way better?

P.S.
I don't want to hurt my boyfriend but I know that is inevitable if I decide to end this. I am also worried he could hurt himself if I leave him, he is pretty self destructive. Should I just stop this and stay with him? I am so confused.
Update: Sorry about where this is categorized. This is the section that was suggested for me. I figured it was more appropriate since the people on this board have been in very long term relationships and know where I am coming from. I don't want advice from single people who haven't gone through this.
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