I would be very inclined to end it. I realise you have talked, etc. and decided to give it another shot.
He found your username and at that point he had a choice (1) to ask you if you wanted to share your posts. Instead of asking, he (2) googled and (3) read everything. Then he (4) talked to his friend about the incident and gave his side of what has happened.
All questions aside of whether the internet is a private place or not, he had choices to respect your privacy and decided not to, four times. Then he lied about doing this.
He seems not to understand that there is a point where he ends and other people begin. A major boundary problem in other words.
' he's quite put out that I told people private things' -- this would come under the category of unacceptable responses to your hurt.
'But I'm too cross he invaded my privacy and think as it's not RL then it's not the same as mentioning private things to a close friend, am I wrong?'
I am assuming you have argued about this point? He has a lot of neck if so. Shameless is the word, actually..
I think you are right to consider it controlling. You have an online support system. You have a right to use it for whatever purposes you want. How comfortable do you feel about using internet support now?
I think it's worth noting that abusers seek to isolate victims from friends, family, support.
I would not give him another chance.