advice - wandering eyes

my fiancé and I have been hanging out with his best friend and his gf. but I kind of get annoyed because he stares at her all the time. someone else in the room could be talking but he’ll still look at her. it makes me feel so awkward cause i know she can tell he’s looking. she’s not disrespectful at all, it just seems to be him. he’ll look her up and down and if I tell him he’s doing it he’ll get so mad and SWEAR up and down that he “didn’t”. but i’m not dumb.... we went for a weekend getaway and the one of the nights we all wanted to go out and smoke at the beach & she didn’t feel good so she didn’t want to come....he was the only one trying to tell her to convince her to come like BEGGING her it was so fucking annoying. like her bf didn’t even want her to go that bad (he’s super quiet and chill all around) she didn’t but then we come back after a while and she finally decides to come out and all he does it talk to her and start walking side by side telling her everything that happened super excited and shit. while we were out smoking we finally go back and she goes to the room and this man literally asks me where is she?? acting like she’s my “best friend” so i guess that means i have to be up here ass constantly ...”did she go to sleep?” i’m like this fucking bitch. i just roll my eyes. idk if i’m over reacting but the eye problem he has is serious. let the roles be switched and i’ll get called out immediately. I need advice please and thank you. I have never really had to go thru this amount of disrespect to my face. I honestly feel so insecure.& I can’t even “say anything to him” cause then i’m super “jealous”. like no all I want is for you eyes to be on ME! why is that too much to ask for.