Summer was a hypocrite
"I was sitting in a deli and reading Dorian Gray and a guy comes up to me and asks me about it and... now he's my husband... it was meant to be."
Well why wasn't it meant to be when they were in the elevator together and she commented to him about The Smiths? Seems like an identical situation. Her "meant to be" explanation is BS. She didn't end up with that other guy because it was "meant to be", she ended up with that other guy because that's who she wanted to be with. And the fact that she has absolutely no empathy or consideration for Tom and his feelings makes her a despicable character.