Do you ever wish you could go back in time and change things?

In June, I thought I was going to finally get a girlfriend, as I was convinced the girl I liked, liked me back and also thought I'd get a good work-placement (a year at university where you work for a company). I'm usually really pessimistic, but things felt so good that I actually got excited and believed I was going to be happy finally, and thought there was no way it could go wrong. But the days ped into weeks, into months without getting a work placement, and without the girl I liked even talking to me. I kept my hopes up thinking it was just a blip. But then I messaged her asking why she wasn't talking to me, and that I didn't care if she didn't like me as much as I liked her, as long as she treated me like a friend (she was my friend before I liked her). And she wrote back saying she cared about me but it would be better for me if she wasn't in my life because it wasn't doing me any good and then 2 weeks later I found out she'd got a new boyfriend. I still kept my hopes up, thinking if I got a work placement in the same city as her, I could try and see her, but nothing came, and now the deadline for a placement has ped, and I'm still single and now have to look for another University course to do. I know its not exactly a heartbreaking story considering what goes on in the world, but at the moment I just feel like a failure, and it's even worse, cos I know the person I care about most in this world, doesn't even care about me enough to be friends with me. Have you ever had this happen?