jQuery( document ).on( 'click', '.love-button', function() {
    var post_id = jQuery(this).data('id');
    jQuery.ajax({
        url : postlove.ajax_url,
        type : 'post',
        data : {
            action : 'post_love_add_love',
            post_id : post_id
        },
        success : function( response ) {
            alert(response)
        }
    });
});

add_action( 'wp_ajax_nopriv_post_love_add_love', 'post_love_add_love' );
add_action( 'wp_ajax_post_love_add_love', 'post_love_add_love' );

function post_love_add_love() {
    $love = get_post_meta( $_POST['post_id'], 'post_love', true );
    $love++;
    if ( defined( 'DOING_AJAX' ) && DOING_AJAX ) {
        update_post_meta( $_POST['post_id'], 'post_love', $love );
        echo $love;
    }
    die();
}