Boyfriend wants to keep looking just in case

My boyfriend of 1 yr (we're in our 40s) wants to keep searching just in case he finds a woman who might give him instant "in love" feelings. He says he wants to make sure he doesn't make a mistake by not continuing to look in case our relationship isn't the one. We have a great relationship otherwise...good communication, deep talks, romance, loving eye contact, great physical intimacy, honesty, and a lot in common. He says he loves me and wants us to be together but still wants to keep looking "just in case"

Is this part of his mental illness or do I need to walk away with my self-respect?

I should add that this is his first relationship other than a long-distance relationship a few years back, and he lives with a lot of fears.