My brothers friend

Long story short he is my brothers friend is like family only to my brother we have known each other but not well since i was 12 i am now 31 we lost touch for 10 years and met each other on a dating app. He was SUPER quick to ask me to spend the night i declined he immediatly wanted to hang out but i work 12 hour shifts so i had little time we hung out once and hooked up 

We hooked up ONCE in November of 2018 but i called off anything more as he is like family to my brother, Plus I started dating!

in january of 2019 my boyfriend and i helped my brother move in, In his new place...his friend was there and was hardcore staring at my boyfriend.... he did not say a peep to either of us.

Anyways, Just now I was sitting in my boyfriends car i saw my brothers friend exit the dollar store...he got in his car and sat there until my boyfriend came out (took about 5-7 mins) once my boyfriend came out and walked to the car he (my brothers friend) sped off really fast

anyways what the hell is his deal?!?!?

I mean I really don’t get why he would be jealous I mean that doesn’t make sense