I think as long as he was in contact, saying he still loved you etc, it wasn't really over and so, whilst you made fantastic personal progress and should ld be proud, you didn't get to heal and let go properly. Maybe seeing this other woman, the way she just randomly intruded into your life and your space really unsettled things, I can understand that causing anxiety. Plus you now have to really and truly have to put it behind you, you know you have to but feel anxious and scared of doing so (hence the blocking and unblocking). Not sure I followed your last post correctly but are you saying he was cheating with her?
My ex left me after 12+ years (together since 16) a week before our wedding for seemingly no reason. Just when I was getting to the point I could eat without throwing up and sleep a little bit without knocking myself out I found out he was cheating, just as I was starting to process the headfuck of that it turns out she's pregnant. Just about killed me, and it took such a long time, I'm talking years, to heal. But I can tell you for sure that that didn't start until we were 100% no contact. To be honest, I got my head round 'loosing' him and not being with him really quickly, but coming to terms with the betrayal, deceit, humiliation and hurt took a really long time. Another thing, and I'm not sure this is true in your case, but I was hung up on the idea of being dignified and keeping the high ground. That's all very well and did save me some future embarrassment probably, but it was only when I thought 'sod that' and got really fucking angry and let myself feel that, that I was able to let go.
Feel your feelings, don't beat yourself up that you 'should' be feeling x y or z, or you 'should' be over it by now. Give yourself a day or two to really wallow, let it in a little bit, I bet you'll find its much more manageable afterwards. Well done on all the work on yourself, keep that up and honestly, really really go no contact. If you feel compelled to message him something text it to a friend instead (pre warn them!) or post it on here.