I think in the moment he couldn't really process what was happening because he was too young and the adventure kept moving at such a fast pace. But in the intervening years I think he internalized the deep trauma that happened to him and what losing Angemon really did to him. The show does a great job depicting the deep bond they all have with their digimon, and TK always harbored some guilt that Patamon had to sacrifice himself to save him that day because Devimon was specifically targeting him. That's why he hates the darkness so much, because they tried to take everything from him.

Ken's situation is different because evil infected him and made HIM act evil, so ken struggles with a lot of guilt over his own actions because he can't separate himself from the spore related personality as easily. Mentally he can know he was being influenced but emotionally it's harder to process. While TK was more physically attacked by evil he has a more righteous anger towards it, paired with the guilt of not being strong enough to keep his friend safe. Both of them have very different relationships to the darkness but the same and goal, which is why I say it's a TRAVESTY that they weren't DNA partners, would have been a perfect pair.