Please help me figure out how exH is spying on me?

She's single. She doesn't introduce the men to her child. She can have a new one every week if she wants!!

He may of spotted you on dating apps, but hidden himself
Parks close to your house to stalk
He/Someone saw you out on a date
He notices your pattern of being out more, if he is particularly has close communication with your son and ds tells him your out and he’s assuming you’re seeing someone.

As others have said, get your devices checked by a professional. Also, your car could have a tracking device. Could he be following you, if he lives nearby? Think carefully about who and where you've discussed anyone you're dating - if it's only via phone messages, I'd start there.

Strength test your friend and give incorrect information to friend to see if that comes back via Ex husband, nothing so significant that it would raise a flag.

Then tech check to see what is installed.

Absolutely change the locks and do not give him a key, you are divorced for a reason stop giving him ground.

Change the locks.
Be careful what you say to anyone, including your child.
Change passwords to everything, log out first. Check all your settings to make sure no one else has access.
If you use Alexa, don't forget to change that too, on amazon.
Take your phone to a shop and ask them to check it for you.
Delete all apps you don't use.

Have a think about how you've communicated what he knows. Have you talked about it in your house? (Unlikely if you live without any other adults, unless a phone call.) If it's stuff that you've only messaged to someone, your phone is the problem.

Although there could of course be devices in your house too.

It's creepy as hell OP, I'm sorry you have to deal with this.

I’d get the camera/ microphone detector. Some are so tiny they could be anywhere. Hidden in child’s toy,in the garden, the list is endless and he could have had things there before you even split up. Good luck.

My dh works in this field.

He said...

remove the key to your house. It's just not needed, especially given your history. It also makes listening devices a piece of cake for him.

stop all chat with the mutual friend.

Check for tracker on car under wheels usually.
Do you have ring? Home devices can be hacked.
Key stoke on your phone /laptop - Get checked.
Once clean - Sign out fully from WA and cloud and resign in and change passwords. You could also get a burner phone sign in on there then log out and reset. But if theres key stroke tech on phones or laptops it wont help long term.

listening devices are a possibility given his easy access to your home but less likely.

Get a burner phone and only use that for dating etc. Do keep using your regular phone as well for normal things so he doesn’t get suspicious. You should also do what others have recommended as well. But use the burner phone on mobile signal not wifi or go to the library and use a computer there to do any required googling. He might be logging into your router.
You should also get this thread deleted asap

Change the locks!
Someone like this should not have access to your home.
You could always have a garden storage box or something outside for dropping stuff.

And then get all your devices to a computer expert.

I also wouldn't trust this mutual friend implicitly, and be careful what you share with them

Also check any toys or electronics that are given as gifts to your child.

Ask for your key back or change the lock. If he was controlling and still is, the last thing you want is him having free access to your home.
He could have put a camera somewhere in your house. It's not unheard of.

Yes. My daughter was in a coercive relationship and so was a tech-savvy friend of mine. My daughter found a tracker attached to her car, and friend found cameras in his home (disguised as electrical plugs, I think). You also need to do a complete "digital detox", take all your devices to an IT expert (could be a local computer store, coukd be a tech-savvy friend) to check for any tracking or hacking programs. Make ALL your devices password protected and use new passwords. I would NOT let him have a key. He us your ex but still exerting coercive control. Maybe you should go to the police.

He may have installed keystroke software on your devices. Then he can see anything you type.

Id take all your devices to a computer repair shop and involve the police if anything is found