Should i forgive him or not?

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We were introduced to each other through his sister. His sister was my friend on social media and she asked me to help him with something I was good at. That's how we were introduced to each other. Then on, we used to talk everyday, we used to call each other and had a good time with each other. He is younger to me, I call him "little one". By that time we were good friends and used to share everything with each other. I used to talk to his sister on social media. Once he even played a prank on me. He chatted with me by logging into his sister's account. Doubtful about the talks, when I asked him he honestly admitted that it was him. I was angry initially but considering him to be the little one I forgave him. But this time I have come to know from one of my friends that he asked them about my relationship status. I don't like people who talk behind my back. The reason he gives is that he was uncomfortable asking me this and so he asked my friend. Now, should I forgive him??