Board Thread:Spoilers!/@comment-25345262-20150308171226/@comment-24674051-20150413143605

First, I don't think Robin realized that Marian had been held as Regina's prisoner.

Second, we are left to assume that Regina actually executed her in the original timeline. We never see the end of the story play out except in it's altared state. Who knows if Marian didn't finally cave in to Regina right before the execution.

Third, as we have seen, Robin himself has a bit of a shady past. (He was a straight up thief, an honest Bar Keeper, and finally the thief with a code that we all know and love). He's gotten a second chance, and his code says that Regina (and anyone else for that matter) gets the same. And let's face it, The Regina he is in love with now is NOT the same Regina that captured and likely executed his wife.