It's good to realize the truth.
Brandon has been noticing his girlfriend go out for ladies night more and more, and is getting suspicious when she starts turning down his requests for sex afterwards.
Brandon wants to have a happy and fulfilling relationship.
Brandon confronts his girlfriend and asks what is going on.
Brandon ignores the signs and never brings it up, hoping that it will pass.
Brandon's girlfriend confesses to cheating on him, they seek couples counseling and eventually make it past this hurdle and live a long and happy life together.
Brandon's girlfriend get's pregnant, and he ends up supporting her for years before discovering the child is not his.