Is my spouse's infidelity my fault because I am seen as not perfect enough?

No; infidelity is a choice made by the one who is unfaithful, and the responsibility lies with them, not you. No shortcoming in a wife or husband justifies betrayal; every marital problem has an honest way to be resolved without cheating. Blaming yourself only deepens the wound and is often used by the guilty party to avoid responsibility. This does not mean the relationship cannot be repaired together; it means the guilt is not your burden. Let go of accusing yourself, and if the marriage continues, repair it as a two-sided effort. A counsellor can help you rebuild your confidence. See counselling.