Initially he said yes for marriage to Ishqi just to make Sonu jealous so that she comes back to him. Ishqi had asked one year for marriage but due to Shekar uncle's heart attack they advanced the wedding. In fact, there is a scene where Mayank was trying to convince Ishqi to say no to marriage so early. It was not very evident but they hinted this.
Later, when Sonu was not accepting his proposal and was happy with Raj, he just wanted to break her wedding. At the end he knew Sonu will not come to him so he wanted his revenge by breaking her marriage. He did not care if he gets married to Ishqi, he would have anyways cheated her with other girls and live his life.
Edited by kankabhor - 4 years ago