why I can't enjoy these things like he does without getting sad/angry
One thing that I had to explain to my W is that while she had three years to deal with this, it is brand new to me. IT also may take me as long to process it to a point where I can be objective.
The other thing is that with someone who does not have the compartmentalization skills that a WS often has, it is impossible to separate the betrayal from every aspect of our lives. Even something as mundane as getting the mail can remind you. Taking a shower, driving. It is something that is subject to involuntary recall for the rest of our lives. It is a memory that they created. We often can't control it until many, many years later.
One of the main struggles I have had is trying to understand a broken/compartmentalizing/selfish approach to things. I had to come to terms with the fact that I may never understand her 100%. I equate it to trying to understand someone speaking a different language.
Now, I had the benefit of working through my FOOs long before this came up, so it might give me a little more insight. However just like we cannot understand what it feels like to be a WS, they have difficulty understanding what it feels like to be a BS.
Just like couples who never gone through this don't understand, someone who has never been betrayed struggles with understanding. Sometimes they give up or put it into a box so they don't have it face it, etc.
The expectation of rational healthy behavior from someone who clearly demonstrates that they are not is what got me.
Now I will also say that people can grow and change those behaviors. Sometimes it takes longer that we want.
Hopefully that reads the way I intended. AT this stage he just needs to know that you are sad. He also knows that he needs to work on being patient and looking to grow beyond his current programing.
It never hurts to mention that you showed tremendous patience by simply not divorcing him and trying to save your M. (Or other examples you can remind him of). If he wants the M it is required that he do the same.