Tell them you LOVE them

Anas RA said that a man was with the Prophet SAWS, when another man passed by.
The first man said, "O Messenger of Allah, indeed I truly love this man."
The Prophet SAWS asked him, "Have you let him know that?" He said, "No."

The Prophet said, "Tell him."

He caught up with him and told him, "Truly I love you for the sake of Allah,"
and the man said, "May Allah, for Whose sake you love me, love you."

[Reported by Abu Dawud, with a sahih isnad]

In another hadith, the Prophet said,
"When a man loves his brother let him tell him that he loves him".
[At-Tirmidhi and Abu Dawud]