First i want to say THANK YOU SO MUCH for this!
It’s like you are reading my story… just today at work I saw a beautiful young women and my mind started telling me that my husband would probably think she’s HOT!
And I proceeded to feel old and fat and all the bad things that make anyone feel unlovable.

It’s nice in a way to see I’m not crazy and not alone! I even was thinking to print this and have my husband read it so he stops telling me I’m making a big deal out of nothing! It always makes me feel isolated when he does that.

2 weeks ago I went to see my therapist and finished my session with the topic of mind wondering about jealousy and envy. He gave me a great advice I had never contemplated before.
I’ll do my best to translate it for you.
First: My Way of handling it…
Those are the steps I’m going through when I’m in that very situation. We are in public or at a party, pretty girl show up – he looks – gets a little distant with me – keeps finding ways to keep looking – I get upset- become independent and frustrated ( miserable)…. basically I can’t enjoy myself and I want to leave- he ask me what is wrong and the argument starts…. Recognize the pattern?!

Alternative: Therapist Way of handling it…
We are in public or at a party, pretty girl show up – he looks – gets a little distant with me – keeps finding ways to keep looking – I get closer to him and smile while whispering ” She not bad, but nothing you can’t get at home”.. Now wait a minute ok, very important to not be sarcastic or mean. Nice and sweet! You can even give him a kiss!- He looks at you and instantly remembers why he loves you so much and kisses you or smiles – time pass if he still staring so you gently grab his chin and make him look at you and say” Hello… moon to earth… I’m right here” and smile 
I think you get the point. Make it a game (it’s not fun I know) but that should shake him a little!
Now I do not imply you should tolerate it by no means – just approach it with a different angle!
He has to be accountable for his behavior and unfortunately when we women engage in that conversation men typically get defensive and go in their famous cave! They are better than women at arguing because they are in it to win no matter what and we get hurt! Nothing good comes out of it.
I did it the last time I want to dinner with my husband and it actually worked.
He felt bad and looked at me and defended himself (nicely) he said ”oh no bb, I was not looking at the girl and blabla… then I walked away and he followed me saying that he was not doing it. I said laughing ”I caught you haha” I said ”I have my eyes on you mister and changed the subject… moments later I had forgotten about it and he came back at me and said ”Bb, I really was not looking that girl up…bla bla bla”
I just smiled and changed the subject. Inside I was not feeling as bad as usual, I think I felt good about the fact that I did not ignore it but I dealt with it differently and showed him that I can be nice about it but I won’t tolerate it!
I hope it helps!
FYI – my first language is French so pardon my grammar… I hope I got my point across!