Is engaging in online sexual activity with a married woman considered adultery, what is its expiation, and is masturbation permissible to avoid such a relationship?

The fornication (zina) that necessitates the prescribed punishment (hadd) is the unlawful penetration of the private parts into other private parts. As for online enjoyment, it falls under metaphorical zina, which is an abhorrent sin and a manifest evil. The expiation for these prohibited actions is sincere repentance, which involves abstaining from the sin, regretting it, and resolving not to return to it, along with concealing one's sins and avoiding the causes of disobedience. Masturbation is forbidden and impermissible, based on the Almighty's saying: "And those who guard their private parts Except from their wives or those their right hands possess, for indeed, they are not to be blamed But whoever seeks beyond that – then those are the transgressors." If you are unable to be intimate with your wife, the path to chastity is frequent fasting, guarding one's hearing and sight, staying away from temptations, and occupying one's time with beneficial deeds, while seeking Allah's help and increasing in remembrance (dhikr) and supplication (du'a).