I think you have to be happy with yourself. Being happy with yourself while in a relationship that isn't working is very hard... but not impossible. So you have your girlfriend and that's just not working on many levels. The old lover situation didn't work out. Meeting this old school friend , Your already saying that isn't working..

Sooo.. Why not just focus on you right now?? Spend time with your horse, focus on finding happiness in your life , as in your own personal life and esteem. Be kind to your girlfriend, don't expect a physical realationship, just be kind, Be kind to anyone you have in your life... At first it may feel forced but trust me it does just become a habit. I am not saying allow anyone to just walk all over you. Just be kind whenever you can.

And first and for most be kind to yourself, cut yourself a break, relationships can come in and out of your life, But being kind to yourself will be one of the most valuable lessons to learn.

Allow some times to decide what you really want for your life. In the mean time go take a ride for me since I can't

You can do this, Be kind to yourself