A) Married because of feeling pity
B) Married because of repentance
And moreover, any one with even the teeniest intelligence will figure out that Karthik didn't "KILL" vijay but it was just a misfortune that karthik went where vijay was supposed to go... to show that Shanti - this fantastic career woman will believe nonsense like this is taking it way too far...
anyway.. she had a NASTY look at the end of the episode.. I would have thought that Shanti would be disgusted at the way Karthik was in Anni Bhakti.. this army incident pales in compariseon