I really liked the post by @opti about coffee and the post that raised the question whether trusting a person as friend and as love are different.
I feel you can trust your instincts but can you have faith in your instincts?no.
which means trust comes from assumptions based on your analysis of a person's character or a situation that you may be in.in nandini's case by now she knows manik is a very good boy large at heart.that he cant harm no one intentionally.so she trusts him as a friend as a human being.but the dhruv thing made her not have faith in him as a lover.
faith comes from dependability reliance and when the trustworthiness of a person is time tested. so time is very important here.nandini trusts manik the friend the person in general but she has little faith in their relationship now.
am sure nandini would realize soon that she needs to give time to their relationship and then faith would automatically seep in their beautiful life and manan would complete each other no self doubt can creep in.