hard to say, really.
my initial reaction is that the weird part is giving your boss a gift, female or male. but that depends largely on the type of job. at a more casual place (like my part time job) we're all friends so it does make sense.
but your situation is a little stickier. on the one hand you do sound pretty insecure. texting about job related matters, and giving her a ride when she needed one sounds like stuff any professional relationship could encompass.
and he did ask you before buying her a gift, so that's something.
but the rest is a kind of suspicious, isn't it? if he doesn't buy YOU birthday gifts it's very odd that he wants to buy one for his boss. and i sure don't like him hanging up on you.
it's all probably nothing, though. i suggest you both sit down when you're NOT upset and talk it through rationally like adults. use 'me' and 'i' statements, not the accusatory 'you.' actively listen by mirroring back each other's statements so you know you've both been heard and understood.
if after that, and your 18 years of history, it's still not resolved i suggest a marriage counselor.
khairete
S.