Hold tight to and understand that just because the grass appears greener on the other side of the fence, it doesn't mean that it actually is. After all, the neighbors could be using artificial turf! I'm going to make an assumptive jump here and say that you'd probably rather have the real thing!
In all seriousness though, I believe the best way to "get over (your) regret" is to pause, reflect back for a moment and ask yourself the pertinent question, "Why?" If you are truly honest with yourself in answering why you didn't move forward with that man at the time, you can begin to use that piece of information to search for the one who has ALL the pieces that make your "perfect man puzzle" complete.
Additionally, take time each day to find the positive in what you DO have. Appreciate the soft, lush grass under your feet and stop looking behind you at the grass in your neighbor's yard.