If/Else Statement for Advanced Custom Fields

<?php
if( get_field('parent_repeater') ) : while( has_sub_field('parent_repeater') ) :

    $some_bool = get_sub_field('true');
    $sf1 = get_sub_field('sub_field_1');
    $sf2 = get_sub_field('sub_field_2');

    if( $some_bool == true ){
        echo $sf1 . $sf2;
    } else {
        echo $sf1;
    }

endwhile; endif;
?>

You must use the non-echoing version of the function. Use the get version. Also, I advise you to use safer name for fields. These seem a little dangerous. Maybe just me.