how do i vocalize this to my boyfriend? having a hard time properly conveying the issue.

background context: boyfriend (M21) and i (F22) are doing long distance until i finish uni (august 2027).

my boyfriend (M 21) got a new coworker. he was already close with four of the old ones, but recently, a new girl (F19) joined their team. they all have gotten close outside of work and hangout every weekend and occasionally, after work.

the girl, S, is an artist and does temporary tattoos for fun. two weekends ago, they were all hanging out and i guess she gave my boyfriend (a very nicely done!!) tattoo on his back... which he was shirtless for.

i would like to clarify my issue does not stem from jealousy. i have formed really nice friendships at my old job and still continue to hangout with a lot of my old coworkers!! additionally, i have a lot of guy friends, and FULLY believe friendships can be just friendships. the problem is my boyfriend tends to get jealous very easily.

if i had been in a bra in front of my guy friends getting a back tattoo, my boyfriend would have been very upset. in fact, this weekend he had me unadd my ex (whom i "dated" for 3 months when i was 16 & we decided we were better as friends) because i had "no reason to keep him added, since i was out of state anyways." whatever, nbd.

i bring up that im upset he sat shirtless in front of his friend because if i had done the same, he would've made it an issue. his response to that was "it's different because i'm a guy and you're a girl. our chests look different. i've also never liked her, and she's just a friend." LIKE WHAT?? a) that's not even what i'm asking b) the argument also applies to me??

what do i even say???