I'm not going to judge you. I will just answer the question you posted for the guys.
Yes you are wasting your time. Not saying he doesn't like you or even have feelings for you but you were convenient. You were there, you were safe. Having business together gave you a reason to spend time together. As a married man he couldn't openly go out and look for other women even if he wanted to. You were the easiest and most comfortable option. Once he's single he's going to have a ton of options. New options, he's had you, no offense. Some of those options will be much younger and won't have kids. Besides, even as a cheater he knows that he can't trust a cheater. You probably know that too.
I know what you're thinking, I know him, we're best friends. Yes honey, you are best friends until a younger, hotter, "best friend" comes into the picture.