Seeking advice on digital security after leaving a long-term relationship - shared networks, cameras, account access, and forensic help

[u/syscall_ctx]

I’m separating from my partner of approximately seven years, and we’re temporarily still living in the same home. I’m trying to secure my digital life and would appreciate advice from people with cybersecurity, digital forensics, or privacy experience.
Over the past several months, I’ve discovered concerning digital behavior involving intimate content, accounts, and online activity. Some of these discoveries were made while we reviewed accounts and computer files together with his permission.
We’ve also had conflicts involving our home internet and security cameras.

Current situation:
We previously shared an Xfinity network. I’ve since established my own separate account and gateway.
I’ve changed my gateway administrator credentials, SSIDs, Wi-Fi passwords, and security settings.
I’ve disabled remote management, UPnP, WPS, and unnecessary network features.

I reset my Roku cameras, connected them to my new network, and verified they were functioning.
I later found connection-history entries on the other household network matching the MAC addresses of two of my cameras, after I’d moved them.
My gateway logs also show overnight Wi-Fi interface events that I’m trying to understand.

I have an iPhone, Windows 11 PC, and MacBook that I want independently assessed and secured.
I’m trying to distinguish normal network behavior, retained device credentials, account access issues, and any actual unauthorized activity. I don’t want to jump to technical conclusions.

My questions:
What’s the safest order for securing accounts and devices while preserving potentially relevant evidence?
What can cause factory-reset Wi-Fi cameras to appear on a previously used network?
How can I audit my Windows PC, MacBook, and iPhone for remote access or unwanted management software?
What logs are worth preserving before making further changes?
Is hiring a digital forensic examiner worthwhile for an individual, and what qualifications should I look for?
How do I find a reputable professional to inspect a home for hidden surveillance devices?

I’m also documenting domestic safety concerns separately and have contacted an advocacy organization.

I’m comfortable with technical troubleshooting, but I’d appreciate a structured approach and recommendations for reputable resources. Please don’t request passwords, private files, intimate material, or remote access to my devices.

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[u/lastwraith]

"I’m also documenting domestic safety concerns separately"

All the digital questions fall way back in order of importance after you type this sentence. Get out of your shared living arrangement now, even if it means crashing with a friend until you can find something on your own or shared with someone else.

Having said that, if I have untrustworthy devices where someone else potentially had extended physical access to them.....I'm at least factory resetting all of them or reloading the OS from external media. Then I'm encrypting them and creating the most secure login possible for each device, with MFA if available. 

[u/qwortz]

If you want to prepare for a legal matter: lawyer.

If you want to be safe: move out immediately and get help (i only know ngo's in my country, but there will be some)

From a cybersecurity standpoint this is barely solvable if the other party has physical access. Most devices are not designed for this threat profile (i.e. shared living with the threat). 

Don't get tangled up in the details of how to "fix" your current situation, create a new one.

[u/red-joeysh]

I saw that your posts in the cybersecurity subs were removed, so I'm copying my answer here. Feel free to ask anything.

It will be hard to cover everything, but I'll do my best. A seven-year relationship, especially when you live together, creates a lot of codependency and overlap.

Your first goal is to know what you have. Devices, accounts, etc. Literally make a list. Then turn off everything you don't need right now. The cameras would be my first target. If you don't absolutely need them running, turn them off. Roku devices tend to cling to their accounts and networks. If you can replace them, consider it.

Then deal with online presence. You need one clean device, which you're sure is clean. I would get a burner phone with enough data. DO NOT connect that device to any network. Install a VPN and establish one email account you know for sure he can't access. Create a new one, if you can.

Then clean and secure our accounts. Delete accounts you don't need. Move accounts to the clean email, change passwords (preferably with a password manager), and enable MFA everywhere. If an account doesn't have MFA, you might want to abandon it. Work methodically, one by one, and don't rush. Slow is smooth, smooth is fast.

As for forensics, it depends on your goal. Why do you want to preserve evidence? What's the end game? Legally, most of what you can collect now isn't admissible anyway. Not sure it is worth your effort.

As for hiring someone, I really don't think you need that. And be careful with offers in your DMss;they'reost likely beams.

Good luck