What I'm seeing is you taking out your anger and hurt and frustration and landing it on people who are by design, supposed to have unconditional love for their family. They advised you to press on, forgive, most likely to forget, the betrayal infidelity has caused.
It's normal to feel exactly what you're feeling. It's ok to be mad and hurt and not want anything to do with the family members who tried to persuade you this isn't a big deal.
Forget them. They do not have your best interests at heart.
Here's the kicker - either does the one who caused this heartache to begin with. You seem to forgive your husband much easier than the people that actually didn't cheat on you. You'll have to ask yourself why forgiveness comes at his family's expense and not his.
It is not your concern how he is perceived by his family - he needs to own up to his wrong doing and atone to you, then his family. Your thought pattern should not have any concern how they think, or feel, about his cheating on YOU. Let them vent to him, advise him, console him and make excuses to him.
Don't let outsiders dictate what happens next. It's not their call.
Although I don't have high expectations of a long lasting marriage, at least know no one can tell you how to react to a misdeed placed upon your shoulders. The decision to stay or go is yours and yours alone,