I think she's not The One for you.
And if she can go out with ANOTHER guy on V Day when her bf is on
guard duty, I don't she why she cannot go out with some other guys
when YOU are busy, or maybe, NOT IN TOWN. 
In my opinion, she's just a girl who's making use of you to spend
time with. *shrugs* Or maybe she's out to sow discord between you
and your best friend!
If you allow yourself to believe she likes you still, good luck.
And I congratulate her for succeeding. I mean, 70% success. Haha..
the remaining 30% will have to depend on your best friend.
And you think your best friend was really cool about the whole
thing? Try it if someone spent V Day with your girlfriend when
you're not around! Even though the other party might be your best
friend, I believe you won't feel good too. So IF you really *think*
your best friend's "thank you" was heart-felt, I
really pity you.
I mean, I won't thank someone who spent V day with
MY girl, when I'm not around. And even if I do, it
won't be from the bottom of my heart. Period.
So I think you shouldn't live in self-delusion.
