[PureStorm]

Well, it's Tom's free choice, but it kinda sounds like he lied to you, saying you were his choice #1, when you actually were #2.
Claire appears to be very manipulative, she may or may not have told Tom things (maybe lies?) about you that made you appear less attractive and less qualified as a gf, while empowering her position as a potential one. To sum it up, she thinks you didn't deserve him. She just took him away. It's out of jealousy, not because she's into him like you. With that said, men together with an attractive women attract more women. But I dont think it was THAT much that she suddenly went from disinterest to enough interest to steal him from you.

My oppinion? Both not your friends. Their behavior is kind of the opposite of what a friend would have done (not saying that Tom would have had to stick with you, but lying + breaking your heart on the first opportunity...think about it).
Hope you find your own truth and make a wise decision to get over it.