I think what you are experiencing is perfectly normal. I have days where I feel dare I say almost happy, relieved he left and relaxed then other days I feel so devastated that I can't function and I fall apart. Others on this forum have said this is grief and I am grieving the loss of my marriage, hopes and dreams. I like you still think at times that if only he would come home and be the man I know he can be, loving and thoughtful but he is at a place where he believes is a drunken B*****d and useless. I can't change how he feels only he can and he won't seek help.
The man I know he can be and want him to be is in my head he doesn't exist and hasn't for a long time but I struggle with letting him go and accepting who he is.
What you are experiencing is grief and it's natural that one minute you will feel so sad that it consumes you and other times enjoy laughing and feeling normal. Take one day at a time enjoy the moments where you feel happy and when you feel sad sit with your emotions, feel them and work through them.
You will come through this one step at a time big hugs