The only way for you to be sure of your relationship with your partner is to sit down and talk to him.
This guy maybe genuine and actualy trying to be friends with his friends " girl " , however taking you out and about town will only cause other people to talk and your boyfriend will here this talk , what he makes of it will be up to his own imagination. " but im sure you can see where im coming from " especialy as this man did not have your number prior to your boyfriend going away.
By all means it is not written that men and women cannot be friends , however when in a relationship " especialy when the partner is absent " , you should be careful not to give the wrong impression. " simply because i see so many people coming here saying he is jealous and i do not know why ". i am guessing here but i think maybe your boyfriends friend is single. i can only imagine how it would look to your boyfriend .
You should talk with your boyfriend and tell him how you feel and find out how he feels and both work from there , involving a third party can only make things more complicated. " im not saying dont be a friend to his friends , just be careful they dont misunderstand or anyone else for that matter.
Hope this helps