<human>: Hello. This is not really important. I'm trying to figure out if this is considered cheating or not. We're no longer in a relationship and I'm just looking for your opinion.

So to the question: Me and my EX broke up for a few days. She came to my place and we had sex, when she left, we we're a couple again. 

The next day I get a text saying she does not want to try anymore. One more day goes by and she has a ONS with some guy. 

I consider this cheating. Because we had been togeather for 4 years, all her stuffs we're in my appartment and even her cats. 
She does not consider this cheating. 

I consider this cheating mostly due to the fact that her shit was still in my place and we had such a long relationship, also due to the fact that we were trying to fix it and had even agreed just 2 days before to try again.
What is your opinion?

I will read your answers but not try to argue or comment on the matter anymore.

Can you condense the text into a few key points?
<bot>: Ex slept with a random guy 2 days after a 4 year relationship. I consider it cheating, she does not. What do you believe?