Hi Peach,
glad to see you, sorry for the reason!
is blaming yourself and being ashamed helping you at all? if not, I'd try and dump it.
he found your hooks and he played you, your red flag triggers went off - but for whatever reason you didn't fully protect yourself from the risk any contact with him posed for you.
I've been known to do similar, and I realised there were a couple of subconcious core thoughts/beliefs I had going on - one was that it was childish and immature to cut all contact with someone, that "adults"" should be able to maintain an aquaintance/friendship no matter how unsuited they are romantically - which I'm told is rubbish, and that there are some people I should just stay the heck away from.
that and I forget/accept intolerable past behaviour too easily in a belief that everyone deserves a second chance/a chance to change/prove they've changed and that if I don't I'm not being fair. apparently that's rubbish too, I don't have to give anyone a first chance let alone a second or gazillionth.
these may not chime with you, but it was very illuminating (and freeing) to work that out about myself (with a therapist
)