I have seen this situation time & time again...and yes I have been cheated on once (although I would define it in different words).

In a long term committed relationship, there are so many worse things that a spouse can do apart from having sex with another person....However, having a surreptitious 'relationship' would be another matter altogether....and worthy of a more in-depth conversation at a later date.

I find it sad that when a partner sleeps with someone outside of the relationship this often negates every good point of the person...all the times they cared for us when were ill, the providing a warm home, them taking on board all our problems, and supporting us in finding solutions, them working tirelessly toward shared financial commitments, goals & dreams...the list goes on. We are all flawed human beings...no one is faultless, and I am in no way condoning a partners choice to sleep around ....But Love is a powerful drug, and for that very reason finding forgiveness for the transgressions of those we hold dear is part of being human too.