Secure My Google & Nest Accounts

I need help to determine if my ex is logging into my Google and Nest accounts. I've noticed frequent activity that I don't recognize. I suspect they might be accessing my accounts through an unknown method.

Requirements:
- Investigate and identify unauthorized access
- Provide a detailed report of findings
- Recommend security measures to secure my accounts

Ideal Skills and Experience:
- Expertise in cybersecurity and account protection
- Experience in investigating unauthorized account access
- Strong analytical skills and attention to detail

Please ensure your approach is discreet and professional.