When a man sends letters and goes on ski trips with a married woman that is adultery.
Yes, it's a species of adultery, albeit more remote from the actual physical act ... as per Our Lord about how one can commit adultery even in the mind.
There are some pictures of Wojtyla on what appeared to be almost a "family picnic", not only with this same young lady, with Wojtyla in his shorts, but also accompanied by a young child, about toddler age, who bore a remarkable resemblance to Wojtyla. I was at a church picnic where a Traditional priest was showing the picture and commenting on it.
Wojtyla had been widely suspected of being a Commie collaborator, a "Pax" priest, even in his day, as while other truly anti-Communist prelates (Wyszyński, Mindszenty, Slipyj, Stepinac) were imprisoned, tortured, and otherwise persecuted, Wojtyla was permitted to go on world lecture tours speaking about the new theology and phenomenology. Not only that, but Wojtyla was hand-picked by the Commie official in Poland to be a bishop. In Commie Poland, they forced the Church to submit candidates for episcopal consecration to the Commie official and have them approved, and Wojtyla appeared on no list, and so the official kept vetoing everyone on every list submitted, until he finally said, quite bluntly, "I will only have Wojtyla." Of course, Weigel, who wrote about this, claimed that "oh, boy did they regret that, as they had no idea what they were in store for." Utterly laughable. They knew EXACTLY what they had in Wojtyla, a Jєωιѕн infiltrator and Commie agent whom they could count on to further the destruction (as they saw it) of the Catholic Church, their once-intransigent enemy.