Why would he do this?

In September 2016 i met this gorgeous American guy, i live in the UK btw. Anyway we hit it off straight away and dated for 3 weeks. Yes we even slept together a few times. He then arranged to meet me and suddenly ghosted me and blocked me on everything. It was the first time id been ghosted and it stressed me out, and i lost 7lb in a week. Another guy asked me on a date and whilst I was on the date with him I bumped into the “ex” and I saw red, I asked him what his excuse was and caught him out lying. Me and the American guy went on a couple more dates, then he ghosted me again.

Since then I haven’t bothered with him. Last year he dropped called me off his work number and I ignored it. He’s also shouted abuse at me in the street when I’ve walked past on the other side a couple of times. Again i just ignore it. Then yesterday I went for lunch with a friend, and in the bar we Saw my American “ex”. He was trying to hide from me as he walked past to order yet he also sat on the booth behind us incase we talked about him, which we didn’t. It was obvious what he was doing and then when I spoke to a friend of his later, his friend admitted that he had told him that he sat there because thought id talk about him and he was annoyed when I didn’t.

Like what the hell is this about?!

Edit- we never actually talk to each other now, if he does say something it’s never nice, he usually goes out of his way to avoid me. I have no interest in him anymore because of his ghosting and his shitty attitude towards me and we are currently both single.