What to do first when you suspect a partner may be unfaithful

A neutral sequence for organizing concerns before confronting, following, or making a quick decision.

Protect safety and daily life

If there is danger, violence, threats, or stalking, prioritize a safe place and police support. In Japan call 110 for an emergency or #9110 for non-emergency police consultation.

Separate facts from questions

  • Changes you directly observed
  • Why those changes worried you
  • What remains unconfirmed
  • What outcome you want for yourself

You do not have to hire immediately

A Diary, a trusted person, a counselor, or a lawyer may be a better next step. If you consider an investigation, compare written quotes and contracts before deciding.

Primary sources

Related guides

Choose your next step

You can start a private Diary, keep reading, or stop here. If you later want professional navigation, review the guide before choosing whether to request an introduction.

Start a private Diary · Explore a synthetic sample · Read the PI guide

Written and checked by Jacob Seiji Skowronek(PI-Thenics) · Editorial policy · Last checked August 16, 2026