Hon it took you 20 years to finally discover this!
You just woke up this morning after 20 years and said "ENOUGH!" ?
Oh I suppose anything is possible, but what is really going on here? I can't help but sense there is a larger force at work here.
Communication is everything in any kind of a relationship. My first advice is to sit him down and explain in detail what it is that is bothering you enough to want to separate yourself from him, his family and his culture. Make it clear that you love him.
If you have already tried that, then your next step is to sit down and have a long, sincere and painfully open conversation with yourself.
"Self, I love the man and I knew of his culture before I married him. We have 20 years invested into one another. Do we have children to consider? If I truly loved my husband does his culture really matter to me? I mean it's just something to do or attend right?"
If you finish your conversation with yourself and your heart and mind agree that it is time to move on, then do just that for the sake of your sanity. Moving on is scary, but as a woman who has done it several times I can tell you it is FREEING and worth it!
What ever you decide best of wishes sincerely.