It's only human to get down sometimes. You don't have to be perfect at all times. Just keep imagining doing as Neville said, 'living in the end of the wish fulfilled', which means whatever your desire is, imagine that you already have it now. Do your best to disregard anything that doesn't contribute to creating that into a fact. Imagine the two of you in whatever the ideal relationship is to you as if it's already a fact now. When that becomes true, there won't be any other girl to worry about, so don't worry about her now. Neville said that imaginal acts harden into facts when persisted in over time, so persist as long as it takes and try not to get frustrated if it takes a while. It's like planting seeds. They take a while to sprout and grow. It's the same with these kinds of imaginal seeds that you're planting to imagine this relationship into being.