['I have a girlfriend, and I would never cheat on her', 'That is an amazing thing. Being cheated on is one of the worst things that can happen when ones enters a bond like a relationship.', 'I agree, I am not sure how people can do that to each other']
I am sure that you two will have a happy and loving life together especially if she reciprocates your desire to never cheat.
I have been faithful to my long time girlfriend. I would never cheat on her