Boyfriend cheating on me with his best friend...?

I have a feeling he's cheating, but I'm not going to break up with him. I have no backbone, and I love him. I'm an idiot blah blah blah. I know. just leave that part out. I'm just hurt, and I need a way to put my mind at ease that doesn't involve me disscussing it or breaking up with him. Is there anything I can do to relieve myself of stress or any relaxation techniques I could do? I really need it. Thanks.