There’s a contradiction here between what happened – something that was intimate and sexual, that you ended in favour of your marriage.
Contrasted with your interpretations of events of being meaningless, not an affair, something you didn’t do and something you’re being unreasonably ‘punished’ for. Is it that the online relationship really didn’t mean anything to you, or was it the case that it was meaningful but you are now seeking to downplay its importance? Do you believe this doesn’t count as an affair because you didn’t have a physical sexual relationship?
Being able to talk through what happened with people taking responsibility for their actions while avoiding blame can be a very tall order - one that is not always welcome when a relationship is in crisis and where those who have been hurt may simultaneously want to both shame and stay with their spouse.
People can get stuck in situations where they deny problems exist or refuse to forgive a partner.
If it meant nothing (as you say) what were the circumstances that led to the online relationship developing and why did it continue in secret? It may clarify things further if you tell each other what you would like to have heard but as yet have not been told by the other in regards to this situation.