I'm not close to my cousins, although we are living in London. All I've heard from them in recent years is an invitation (which never actually arrived) to a 40th party about 5 years ago which I heard about from my sister, and it was too late at that stage to go, and now an invitation to another cousin's big birthday, the invite came via another family member telling me about it and that I was welcome. We have never been close and don't see each for years at a time. I was surprised to receive latest invite but am inclined not to go - AIBU?