I'm sorry to hear this happened to you. I once had a unrequited love situation (however I was used for sex and then ignored) and it tormented me for months.

There's really not much to salvage though. You may have been friends, but romantic feelings got in the way and, you were right, that cannot continue. If you see her, be polite or if you must, just try to avoid interaction. Being rejected hurts but it happens to everyone sometimes and you do eventually move on. Relationships with that kind of age gap are considerably more difficult and many eventually end. I am in my mid 20's. I know girls my age that have dated men in their 40's but it has always ended at some point. :/ My blessings go out to you~~