Could be, but I wouldn't think too much of it. I almost think this may be a good thing--he knows you're not always available.
Quote: H was furious that he did not get a special invite.
Maybe apologize and validate his feelings? He's telling you (okay, in a very angry way) that he feels like he isn't welcome in the house. The next time you have a get together, you should make sure and invite him. And apologize for your SIL's comment! You want to try and make him feel like you're "own his side."
