I think the OP is being given an unnecessarily hard time.
There was a concert, they talked about going. Whether he wanted to take her or she wanted to go - it's all semantics really. The fact here is that they discussed going to the concert together but they left it too late to get tickets and then dh's friend who was running the door said never mind, he would just let them in. Then it turned out he couldn't but one ticket came up for sale and the DH bought it saying "I'll buy another ticket somewhere and if I can't get one then I'll sell the one I've got."
So time moves on and it turns out that he can't get another ticket, so OP says "you should sell the other ticket," except that he then decides that he doesn't want to sell the ticket and he goes out alone with the couple's friendship group.
IMO the point at which things should have been done differently was the point where only one ticket came up for sale. At that point, given they were planning to go together, they should have discussed, and either agreed that one or the other would go with just one ticket, or not bought the one ticket in the knowledge that another one might not come up.
If my partner bought just one ticket to an event saying he'd try and get another one and then didn't and went out without me with our mutual friends I would be thinking that he'd planned it that way all along and never wanted me to go in the first place.
It's hurtful. No of course there's nothing wrong with individual partners going out with friends on their own but to plan an evening out and then make it so only one can go and the other is left out seems a bit underhand.
Also, if you're part of a group of couples and all of those couples go out together and you end up being the only one left out it is hurtful.