Is it midlife crisis?

I will be 40 in a few months. I am married, but a very young guy has started flirting and courting me. He's a typical cool, bad boy. That made me realize that I really like this type of guy. My husband is the complete opposite. Sometimes too serious. I love him and for some reason I married him, but lately he's not cool at all. He is always worried and tired. I told him that and my husband said he is trying to change. But so far no results. And this guy... Or am I just feeling this now?

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I don't want to cheat. I want these feelings to go away. I hope they're just hormones and will subside. Anyway, my husband and I have a good sex life.
Is it midlife crisis?
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