L.L.
Usually jealousy stems from insecurity, and unless you are a naturally insecure person who cannot find favor in herself, then there is a reason you are insecure. You say he hasn't cheated...but what aren't you saying? That you think he COULD cheat? If not, then you need to convince yourself otherwise.
My husband is very good looking, and was when we met 15 years ago in high school. Back then I was jealous because I thought, "Why in the world me, when it could be so and so?" He may have felt the same way about me...but more to the point, we are married, it's 15 years later, we have beautiful children, and I am totally secure.
How long have you been together? Are your children with someone else? How old are each of you? Etc, etc...all of these things are dynamics that come into play. Is marriage in the future?
And a bit of advice...men are generally turned off by insecurity and jealousy, but are attracted to a confident woman who knows (with humility, of course) what she has going for her.