Why is my boyfriend jealous all of a sudden?

Anonymous
My boyfriend & I have been together for over a year. Our relationship is great & has so far been very healthy. We all get a little jealous, that's normal m. But he has never been the "jealous" type. However, the other day, I sent him pictures of celebrities from google bc he can't decide on a haircut & I wanted to show him examples of men's haircuts that I thought would look good on him. Anyways, he got pretty jealous & his tone changed real quick which was very odd for him. What could cause this sudden behavior?
Why is my boyfriend jealous all of a sudden?
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