I'm not saying that you need to immediately cut off contact, because I realize you're not going to do that anyway. I'm just suggesting that, in addition to continuing your hopeless platonic relationship with her, you could also date other women. As soon as you meet somebody who makes you happy, you could just focus on that woman instead of this frustrating, platonic relationship. Or there is even a small chance that she will become interested in you once you are dating other women, though I don't think that you should worry about that. Besides, she's five years older than you, and women usually want the guy to be the older one.
Good decisions come from experience. Experience comes from bad decisions.