How?!

How do you let go the past? How can you even live the present moment when all you’re thinking about is that summer day when you went out together, had the best time and laughed, but then, nothing else happened, realising that he is just not that into you. How do you go further when all you want is to go back in time so you could repair some mistakes you did, some words that you should’ve leave unspoken? We are all wondering why that, why so, why this... but why do we bother so much for people who don’t give a sh*t on what you think? How?!