I was in the same boat years ago. Was going through 125 IOT for GD/P, got backcoursed and then VW'd in order to go through BA cadet selection. Passed that, got class 1 medical and uniform fitting, then got binned at the 11th hour due to the BA final review board deciding I was a training risk due to having jacked-it at Cranwell. Contemplated returning to IOT a couple of months later, and OASC confirmed there would be no problem doing this (they were even going to put me back on the same sqn, possibly with the same Flt Cdr), but in the end I decided to go to uni instead.
Went to uni, got a degree, got back into civvy flying. After a couple of years at uni I started to have regrets, like yourself, and contacted the RN with a view to joining the Fleet Air Arm as a pilot, as well as rejoining the RAF as a nav. Both services said 'forget it mate'. I was 24, there were barrelloads of young keen 18 year-olds with mega aptitude scores out there, and so there was no way they were going to entertain me having already binned things 3 years before. I'd had my chance.
Now, (15 years later!), anytime that my decision to leave the RAF is brought up at an interview I can truthfully say that I was too immature to handle the pace of IOT at the time, and that it wasn't for me.
I have had a successful civvy flying career for quite a few years now, and looking back, I rarely regret leaving IOT, except for the odd twinge when I see a fast jet snotting down a valley somewhere ( and realising that one of the blokes I knew from IOT was synchro lead in the Reds a couple of years ago...). If you want to fly aeroplanes for a living, go for it. The Mil isn't the be-all and end-all, but if you are thinking of going back in, do it now!
ST