What would you do after knowing that your Girlfriend/Boyfriend is cheating on you?

If I KNEW (not the same as "suspected"), I would end the relationship.

This is someone who is too selfish to love.

Love is not a feeling .. it is an action, and if someone does love, they don't do things that will hurt their partner.

Don't waste time with people who don't care about you enough to avoid actions that will seriously hurt your feelings (no relationship is perfect, so we always WILL have some hurt feelings .. but cheating is a selfish betrayal, and a deliberate hurt .. and that deserves to be walked away from permanently).

Realize s/he is not for me.

Leave.

A one off situation msy be discussed and dealt with.

If ongoing, move on

A liar does not deserve love. Would break up with him/her ASAP.