All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
There are two ways:
First: to tell him verbally that you love him. There is nothing wrong with doing so. Since this act is permissible with a brother or sister in Islam; then, a husband is worthier of hearing these words. Anas ibn Maalik said: “A man was with the Prophet, sallallaahu ‘alayhi wa sallam, when another man passed by and the former said, ‘O Messenger of Allaah! I love this man (for the Sake of Allaah).’ The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, asked, ‘Have you informed him?’ He said, ‘No.’ The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, then said, ‘Tell him (that you love him).’ So he went to the man and said to him, ‘I love you for the Sake of Allaah’, and the other replied, ‘May Allaah, for Whose sake you love me, Love you.’” [Abu Daawood; Al-Albaani: Hasan]
Second: to tell him that you love him through your actions. This could happen by obeying him, being keen to please him, being good company and being a good wife. It is said that the lover follows the one whom he loves. It should be known that obeying the husband in good matters is obligatory, even if there is no love.
Allaah Knows best.