Why is this my fault and why is he annoyed at me?

Well, first off it sounds like you are better off without him in your life anyhow. He sounds like the type of person that would easily get upset when things don't go his way., and he takes his ball and goes home.

You had stated that you predicted she would decline. If you told him that, then he may be thinking you did something to make the prediction come true. I'm thinking she might have declined because she can sense he's a loser.

I would stop the messages and phone calls. I would not answer his messages or calls either, once he gets over the baby tantrum he is throwing. Just move on with your life dear, as there are plenty of guys out there for you.

Apparently your partner was a lot more invested in getting to be with this person than in having the threesome for the two of you. And unfortunately, if he won't talk to you about it, then you don't really have a relationship left to salvage. Tell him that either the two of you need to put this behind you and move forward, or you need to move on so you can find someone who can not only handle disappointment but will communicate with you.

A friend can refuse on various grounds, but in a way, perhaps it was best there was a refusal. Threesomes are a fantasy which in some cases wreck a relationship.

He's annoyed with you because you didn't fulfill his fantasy. He's either a douchebag or a spoiled wanker but either way, it's his problem not yours.