My ex husband logged into my laptop and got into my google account. I didnt know at the time, that my found followed me wherever I went.
That's how he could follow me.
It's entirely possible that he has been.
I cant believe you didnt think it was odd that he knew everyone you dated. Despite them saying they didnt know him.
If he has been doing this, he has been doing it since you first met. How would he have got access back then?
I do have to say though. If a poster came here saying her boyfriend said he was going out for dinner with a male friend, then got an uber to pull up round the corner of the house and actually went out with a female friend. Mn would be telling her, he was cheating.
He absolutely shouldnt be doing what he is doing. No excuses.
But I get the feeling you havent never really wanted to be in this relationship and he knows it.
It's better for both you that you leave.
Personally, when it happened to me. I voted a new phones got a new google account, changed passwords on everything.