Personally, i think feelings can 'regenerate' only for certain reasons


number 1:
they recently, or has always, been spending time together and she realise she still has feelings for him

number 2:
she never did forget him even when she's with you

number 3:
might be an illusion, sometimes pple can get confused and think that they are still in love with their ex but in fact it is nothing. For e.g. if your ex goes out with another girl, one might feel uneasy, but that doesn mean u still love her right
