What do you tell a mother who's son died?

Last year on March 30th my late boyfriend committed suicide. We had only been together 8mon and it was a messy emotional and physically abusive relationship with and ex wife and kids involved. I was in the wrong place at the wrong time I guess you could say. Sad to say but I'm over it and I'm moving on with my life. However I've been there for his mom a little this past year and I didn't call her on the 30th I know she is going to wonder why. I just don't feel like talking to her and dealing with all the crying. So I was going to just send her a simple card that will come later in the week. It will be better that way since she was probably bombarded with calls and gifts. I just don't know what to say to her, how do you even start a letter like that? I'm hoping it will be my last letter and she will realize I've moved on and will still hold a place in my heart for him but I need to carry on with my life, and my new wonderful relationship. It's such a touchy topic I don't think anyone really knows how to go about something like this. I don't want to sound cheesy or cliche I'm sure she got a lot of that.