The anurag who did had was the anurag of old, the one who knew who he was what his position was in society and his role towards his family. The guy who didn't believe in love.
Yes he took great effort to help prerna when she got into the Naveen mess but as he said then he doesn't make friends often and when he does he does his duty towards them.
Five days after getting engaged to mishka and then breaking it (only to mishka) to express his feelings for Prerna, he now has broken his relationship with Prerna. Why? Surprise surprise because of his obligations towards his father, Rajesh and prerna.
His first instinct is to give up on the love he has only felt for a few days and focus on fulfilling his obligations. This is not a man who really believes romantic in love or even feels it to great depth. He sense of responsibility and obligation is too strong for that.