How Can I Prevent People From Taking Advantage Of Me Constantly And Not Live In Regret?

Everyone I have been dealing with in business has been letting me down in so many ways that I just want to disappear. I am constantly sorry dealing with people after losing my money, energy and time. I am losing with each and every single one of them. I am constantly making mistakes with the people I choose to trust and work with. I give more respect to these people than I give to myself and then they spit on me or rudly ignor me and take the money and literally run. I have robed myself of too much all the time and I know better but I give people the benefit of the doubt anyway. How can I change and what can I do to stop being so nice to people who don’t care about me.