Speaking as someone who's been on the receiving end of cheating, there's only one way I can describe it. It's like waking up from a good dream and realising none of it was real. It strips you of trust and confidence, makes you wary of other people and distrustful. Being dumped is bad enough, everyone goes through that at some point, but being lied to about something so very vital to your existence is a hundred times worse.
Probably my own temperament that causes me to have such a bad reaction. I fall in love easy and fall out very hard