Why am i so jealous over my fiancee's male friend being with her all the time? Advice?

I am 29 and engaged to the girl of my dreams who just had our first baby in December, she is 26 and i have been with her since i was 19yo. I am a firefighter and work shift hours so i try to make the most of the time i have off and be with my son and girl. I wanted to be a father for so long, i honestly couldn't wait but my fiance wasn't that bothered. She suffered Postnatal Depression and is on tablets that make her very tired. She comes from a very dysfunctional family but all her siblings are very close and protective of each other mostly them with her as the are over 6+yrs older than her. She works in the city and has a great job, she is best friends with a openly gay male who she works with, he is really in you're face gay but i cant help felling jealous of him for being close and spending more time with my fiancee than i do because of work. She hangs with him nearly everyday, she rings/texts me to tell me my son and her are going into the city to have lunch with him or go shopping, I sometimes have to bite my tongue and try not get pissed at her, though other times the 3 of them come over to my job so i can see my son and they are always laughing, that gets under my skin. He is my sons godfather and i do like the guy but half me hates him for being were i should always be. I love my job and can never imagine doing anything else its been in both mine & my fiance's family for generations and its all i know so i will never stop doing it. The other day when i asked her to drop somthing over to the firehouse that i forgot she brought the wrong thing and i told her she has a brain the size of a fish and she called me and a*shole and left, part of me wanted to hurt her & i don't know why. Im happy she is getting back to herself and is happy but i cant help feeling jealous all the time. Just the sight of her makes my day and i hate being this jealous. Any advice?