My boyfriend/partner's brother contacted him midweek asking if he's free tomorrow. He said he was and they've arranged to go for a drink. He's assumed I'm included and is insisting I go. I'm assuming I'm not because I wasn't mentioned in any of the messages.
Boyfriend's sister in law will be there but they've been married for 20 years and so they obviously all know each other well. I've met his brother and his wife twice and very briefly.
Boyfriend won't clarify because he says it obvious I'm invited. I don't think it is.
YABU - of course you're invited
YANBU - I wouldn't assume I was invited unless specifically mentioned.