Glad you found some value in it. Good luck!

1. Don't internalize this rejection. She just got out of a long term relationship. Probably dealing with a lot and the timing honestly sounds awful to me.
2. The fact that you are able to build and maintain a long-term friendship with someone of the gender you're interested in is already a good indicator that you can be in a successful romantic relationship.
3. What doesn't bode well? It sounds like you're into people who are unavailable/unattainable to you.
4. Friendships don't have to end because of situations like that. If you genuinely value her as a friend (not just a potential partner) and you are open with her that you want to continue the friendship ya'll can recover if both parties are mature enough to do so. Some of my longest friendships went through this very awkward experience. Just make sure you are able to actually be a friend though and are not sentencing yourself to be in a friendship where you are always pining for something more or being resentful.