man, you've got it rough! I congratulate you for being able to get it together and didnt spit one of those "it's very hard for me" "it hurts me a lot".
Try to be gentle with yourself and get over her. She pretty much cheated on you, i assume. I suggest no contact with her, no get back together which i think would probably happen very soon when she realizes they both sucks together.
keep it simple
Self-esteem isn't bragging about how great you are. It's more like quietly knowing that you're worth a lot (priceless, in fact!). It's not about thinking you're perfect — because nobody is — but knowing that you're worthy of being loved and accepted.
"Me, I try to send this note
float it like a paper boat
But paper sinks
and words are weak
i try, but i cant speak"