My friend is really making me mad?

I've been riding my neighbors horse for years now and I have a great bond wih him, my friend leased him in June, But she got mad at me when I rode him so I stopped Riding him, but now he is a little bratt again because she cannot handle him, at all. I talked to the owner of the horse and now we are both doing a half lease, she was very happy that I will be riding him again besides the other girl cannot et out that often, but I'm always there because I keep my horse there too, we are showing this summer I am the one who is paying for the trailer I already payed my lease this month and she didn't, I know we both have rights to him, but I'm practically the one training him, and we will be doing western and english she has never done any western but she wants to do amature barrels and pole bending and 3ft jumpers. Which is what I wanted to do, she has oy ever jumped him over a small vertical and never a course, but I don't want to be a ***** about it it just makes me angry , plus I can't use my horse because he is only 3:/ so I'll probably be leasing him for a while