Can I legally fire my personal trainer?

I am an international-level athlete, and I needed some help with form in the weight room, despite having my own running coach. I met with this guy, he said he needed 6 months ( to the end of my season) to get me as strong as I need to be. He quoted me a total cost, but in monthly payments. I started working with him, had initial improvement, but then found him extremely overbearing, judgemental, and pushy, questioning all my other aspects such as track workouts (and that I should skip running to do weights instead). He was even making commments to some of my competitors regarding my abilities. It is doing more harm to me than good, and he is causing me undue stress. After confronting him 4 different times, him apologizing, but then doing another innappropriate thing, I would like to part ways. My season is important, and it's coming to an end quicky!
Can he sue me in small claims court if I never signed anything?
He is a "freelance trainer", and doesn't belong to one gym.

If you or your agent are paying him, you can fire him.
You are his employer, he is your employee. You have full legal freedom to fire him. You have plenty of experience with him that even if there is a contract, there should be no argument in letting him go.