Who is at fault is the affair? Did their spouse drive them to it?

If spouse A is sweet caring and romantic and spouse B complains about everything constantly wants more and more from spouse A, but everything spouse A does is not good enough. This constant complaining makes spouse A resentful and distant. Spouse B doesn't like how spouse A is not as attentive, so spouse B has an affair because they believe they have a right to be happy. So did spouse A drive spouse B to have an affair?