I am so sorry. I completely get the confusion and anger you feel - I just shred 15 years of photos after i found out.
My advice, and you can take or leave it, is to not see him when you're angry. Take a day or two to calm down and get your head straight so that when you do face him it is with dignity and grace. Be the better person. Easy, and you've read my sitch so u know that I am better at giving advice than taking it. Dont make the same i did.
In response to why they keep switching personalities - it is because they live in a fog. Their heads are scattered. Sometimes they feel guilty (and resent you for it), sometimes they want to pretend all is well, and sometimes they want to come home, so they say nice things to test the waters. My favourite saying here is believe nothing they say and half of what they do.
Know what you want and stand firm with as much dignity and grace as you can muster.
