SUBREDDIT: r/relationships
TITLE: Is it appropriate for someone with a SO to meet people of the opposite sex at a party, exchange numbers, and hang out 1 on 1?
POST: I want to hear both male and female sides of this. Ill try to explain my particular situation without gender to get both sides of the coin. 

Recently my [24m] SO [23f] (dating for 4 months,  exclusive for over a year) met a person of the opposite sex at a party. I was not at the party as i live several hours away from my SO. They hit it off, both are dating someone else, and have a common interest in a certain type of music (the person is actually part of a local band). They exchanged numbers and have been talking unbeknownst to me for a while. My SO and i went to a concert the other day and the person from the party was there texting them about it. Nothing came of it. Now i am back several hours away and this person is inviting my SO to concerts with them. Additionally this persons band has a show in about a month and is inviting my SO to attend it with them as what sounds like a vip. Im not overly jealous of the situation,  but somehow it just doesnt seem quite appropriate to me. I just want to hear what others think about it.
TL;DR: 
So went to party, met member of opposite sex, exchanged numbers, person is trying to hang out 1 on 1. Is this appropriate or do i have right to be slightly concerned?