It sounds like the guilt is exacerbating the situation by keeping you increasingly occupied with this other person. The surest way to remedy it is to remove yourself from that environment; easier said than done, of course, and September is a long way off.
Moving on is a difficult process that you'll just have to bear. There's no way to skip through it. But stick to your resolve, hope for the best and you'll no doubt come out a richer person at the end of it.
