Your husband sounds awesome and he is right when he says to open up the flood gates and let it all out. You've been through a lot and what you're feeling is absolutely normal.
I am so sorry that you have lost a loved one. I lost my mother to cancer 7 years ago and I remember it being so so difficult. My thoughts are with you during this emotionally trying time. I always found that it was easier when I was with other people. Of course, I now know that was just a distraction to keep me from having to face my own grief because once I was alone and by myself, the sadness became overwhelming.
You may wish to seek the assistance of a therapist or a grief counselor. Not because there is something wrong with you (there DEFINITELY isn't anything wrong with you; it is normal for grief to feel painful), but because talking with a trained professional can help you start to process what has happened. It can be a very healthy thing to talk about your feelings, admit anger, sadness, frustration, grief, despair, and other emotions with someone who can talk you through what you're experiencing.
Finally, it is okay to break down in front of mom. Chances are she is feeling the same way you are and by being your true selves around each other, it can open up a dialog about the past, the present, and the future without dad. The two of you will always have these special memories of your loved one and they will forever live on in your hearts and your minds.
When with your husband, just let is all break down and let him hold you and listen to you while you cry, sob, shriek, whatever it is you want/need to do. The emotional release can be great for the mind and the body and you may find that the comfort he provides is the soothing you need.
Best wishes to you. I am so sorry that you lost such a great man and family member.