Jealousy in an Amish community is theoretically possible. Practically — pointless.
Why
Everyone knows everyone. If Josiah talked to Rachel by the well — Sarah knows within an hour (community is a giant chat without internet). Hiding an affair — impossible (30 families, 200 pairs of eyes, zero privacy).
Infidelity
Extremely rare. Not because Amish are saints — because there's nowhere and no one. All women are friends' wives. All men are husband's friends. Motel — 20 miles by horse (4 hours). No car. No phone. Tinder — what's that?
If It Happens
Scandal. Repentance (public, on knees before community). Forgiveness (required — but hard). Divorce — no (impossible). Then: live. Side by side. In one community. With the person who knows. And people who know that he knows. Punishment isn't shunning. Punishment is shame. Forever.