OP, the thought that he is monitoring you seems pretty compelling at this stage, the fact that you've found nothing conclusive/no hard proof is serving as a bit of a red herring.
I think you need to assume he is monitoring you, in which case, you need to not talk about anything you don't want him overhearing in your home, in case there is a bug. You also need to not act in a way that would cause suspicion, so having a contractor in to look for bugs or searching for them overtly is not a good idea. You need to do a convincing spring cleaning.
You also need all new/clean tech. He might have software/apps installed, or key loggers which would pick up on new passwords and he would then have and use them. He might be hacking you at cloud level, which sounds likely given all the associations on your computer. You need a new, trusted device that you set up with a brand new email account/icloud account/usernames and passwords to everything. ONLY use that device and those new usernames to look at websites that suggest you're seeking help, posting about your suspicions etc. Assume he will be privy to everything and anything except the clean device.
I'm not scaremongering, I have direct experience of all of these approaches to spying.
Or, just end your relationship and then you can search for bugs/hacking as clearly and obviously as you'd like. You have no trust, he treats you badly, you think badly of him - that really isn't a good foundation for any relationship, nor something that sounds recoverable.