If a man cheats, is it his fault for not being loyal to his wife, or is it assumed automatically that the wife did something to "make" him cheat?

Similarly, does the same belief system apply to a cheating wife? If a wife cheats, is it her husband's fault for failing to be attractive enough or for somehow driving her to it, or should she take full responsibility for her own selfish actions?

Or- do you think it depends not on the gender, but on the situation? Is it possible that one woman could cheat because of her husband's negligence/letting himself go, but another woman could cheat just because she's a selfish, immoral person?

TRP, TBP and non-pill opinions all welcome.