Peace be upon you. If the intention behind this phrase is to express deep love for Imam Hussein (peace be upon him) or other infallibles (peace be upon them), similar to how a mother might say to her son, 'You are my only love,' or a husband to his wife, 'You are the only one in my heart,' then there is no objection to it. It seems that this is the intended meaning, and it does not imply that there is no love in his heart except for that of God Almighty and the love for other infallibles (peace be upon them). May you be successful in all good.