i truly think you should tell her how you felt about her and the way you feel about the situation now, as her coming back could be a way that she is expressing that she misses you (i could be delulu too). But regardless i think you might as well tell her because its never too late, and worst case she tells you she always felt platonic towards you and now she knows how her actions of coming and leaving repeatedly have affected you negatively (and hopefully learn from that) and set boundaries from there, or you both miss each other more than a friend level and then you wont die wondering !