Mind you, I find the whole thing staged for the ratings in regard to Frank and Ali, but there are some things people forget.
This show, as mentioned elsewhere, allows the contestants to leave the show for whatever reason if they do not think that the bachelor(ette) is not for them. This way people aren't strung along.
This is not the first time we've had any contestant leave the show because they didn't feel 100 percent certain they'd be happy with the lead here. It IS however the first time it's been so close to the finals. Even with the fishy nature of this one, it's still a choice based on his feelings that he was making a mistake.
And, in a way Frank did to Ali what she did to Jake - left for what the bachelor(ette) saw as a petty or selfish reason. Of course, Ali seems to have amnesia to that fact, but no - it's quite similar save the reasoning.
In fact, IMHO I think Frank's reasoning made more sense than Ali - who left for a JOB (not questioning lives together, her job), and even came back realizing her "mistake" but it was too late (fortunately/unfortunately up in the air). Or in short, I found her reasoning a little bit more selfish when she did return.
I wouldn't even be surprised if Frank did return and try to get her hand and she say no like Jake did her (and I think he regrets it too). I just find the incident ironic.
As far as the final two, they are both worthy of Ali's hand IMHO. Of course, there is a chance she'll choose neither.