I echo what AnnabelMore said.
In the meantime, I would urge you to go out with friends when your hinge is going out with the other arm of the V, so that you don't end up all alone.
Or if you stay alone, to have plans (go to a movie, or watch something at home), in short keep busy so that you miss him less.
You could invite friends over and play games or something like that.
After all, if your hinge had to go out for other reasons (business meal for instance) you would have to deal with the same feelings. So I think similar solutions would work there.
And whenever you can go out with them or invite the other arm along, feel free to do so. You don't have to be dating to be in a relationship, even if that relationship is friendship. It might not be a full-on triangle but it can get closer to one. As long as you give them time to be alone together, spending some time with the other arm or with all three of you together could help you.