“What does it mean if I dreamed my partner cheated on me?”

The first reaction is usually to be mad or suspicious of your partner. But hold on! While again anything is possible – do your fact checking if you think they are literally having an affair – HOWEVER…This dream usually indicates that you are feeling cheated out of TIME with your partner.  So first ask yourself, has he/she taken up a new hobby? Working longer hours? Travelling without you? Anything that takes your partner away from you can feel like ‘the other man or woman’.  Even an illness, disease, or condition like depression can feel like something (translating to someone in the dream world) has taken away the closeness you previously shared.
Before jumping to the literal explanation, see if the metaphor fits.