It sounds like you are entering a time in your life when you will be doing a tremendous amount of growing and soul searching. Out of every tragedy comes growth and definition. Your situation is a rough one and I'm so sorry you are going through it alone. But, by going through this emotional time on your own, you WILL become stronger, and you WILL re-define yourself. It sounds like you are a strong person, and a kind-hearted one as well, and you have the head on your shoulders to break through this.

You BF sounds like he needed to do some growing too...the excuse he gives is kinda vague...how long were you together? Unfortunately, as we all know, when it rains, it pours! Keep your chin up- you gave that dog a wonderful opportunity at life, and you made the selfless decision to end his pain. That, in itself, makes you a strong individual.