compliments_only_for_friends.php

<?php
function custom_bp_compliments_add_profile_compliment_button() {
    global $bp;
    if (!is_user_logged_in())
        return;
    if ($bp->loggedin_user->id == $bp->displayed_user->id)
        return;
    $is_friend = friends_check_friendship($bp->loggedin_user->id, $bp->displayed_user->id);
    if ($is_friend) {
        bp_compliments_add_compliment_button();
    }
}
remove_action( 'bp_member_header_actions', 'bp_compliments_add_profile_compliment_button' );
add_action( 'bp_member_header_actions', 'custom_bp_compliments_add_profile_compliment_button' );

function custom_bp_compliments_add_members_compliment_button() {
    $bp_compliment_member_dir_btn_value = esc_attr( get_option('bp_compliment_member_dir_btn'));
    $bp_compliment_member_dir_btn = $bp_compliment_member_dir_btn_value ? $bp_compliment_member_dir_btn_value : 'no';
    if ($bp_compliment_member_dir_btn == 'yes') {
        $args = array(
            'receiver_id' => bp_get_member_user_id(),
            'sender_id'   => bp_loggedin_user_id()
        );
        $is_friend = friends_check_friendship(bp_loggedin_user_id(), bp_get_member_user_id());
        if ($is_friend) {
            bp_compliments_add_compliment_button($args);
        }
    }
}
remove_action( 'bp_directory_members_actions', 'bp_compliments_add_members_compliment_button' );
add_action( 'bp_directory_members_actions', 'custom_bp_compliments_add_members_compliment_button' );