I have a different opinion here ...If it was just necessity then any girl could have replaced Sona in his life .Natasha was a understanding girl as well and she would have provided the much needed support to him .since it's love no one could take her position in his life even when he saw her with Ritwick he could not think of marrying or dating any other girl .
There is Tina in his life who is shown to be understanding and has supported him during his tough times .During breakup she was shown to be the one supporting him .If it was not love then he would have found solace in Tina or Natasha or any girl