In a sense it is more His fault, than hers, assuming shes not married herself, she’s not the one who made the commitment to someone else, nor the one reponsible for the kids (if any), hence she doesnt have to think twice. She will probabaly just wreck her own life, he on the other hand will wreck everyone elses…so if anything, he is the essential ‘homewrecker’ who is at fault here.
Same goes for married women with single men.