I've been thinking about this case once more.
What is so bad for the GF about this deal:
"I'll buy you a ticket, but when I get an upgrade I will take it."
The alternative could be:
"You buy your own ticket, and when I get upgraded I will give it to you."
A-greed!!! ^
Selfish about upgrades?! FF programs are individual; the whole idea is to reward that particular person... they're selfish by nature. FF benefits do not extend to family/friends. My fiancee and I have often discussed this and we are in agreement. If on a flight together I score an UG, then I take it, because.... I'm a FF and for her flying Y is not really a big deal.
As to the situation presented by the OP: HE paid for her ticket. Not only is a free flight (or free anything) something not to complain about, but he got the UG as a reward to him as a FF, which she is not. Giving her the UG is an unfair expectation. Yes, it would have been nice, but certainly not something that should be
expected. She's not entitled to that. Getting a free ticket IS nice!
Dumping him for
that?!?

There must be some very lonely people here. Am I getting this right? So you live together, pretty much share your life with someone, but then decide to dump that person because a nice gesture wasn't nice enough? HA!