Do marriages or relationships really last forever?

So my parents recently got separated and it was their 20 year relationship and my father who is a subhuman actually cheated with one of his beautiful colleagues. ( hope she leaves him soon) after that i have become paranoid that in future whomever I'll get married to will eventually leave me and my future kids causing them great trauma. And i think about it every second and I've started being afraid of man. i believed my father too much can't think that he could leave us like this. Any kind of opinion appreciated.

Do marriages or relationships really last forever?
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