I do understand how you are feeling right now. I've felt the same way while looking at some old pictures.... it's really something when the old memories come flooding back.
I'm glad you are saving those letters, I think they will have a lot of value someday in the future.... and yes, maybe your sons would like the validation too.
Honey, I can tell you, you will not end up bitter and angry, you've been working through this all along, feeling your emotions, taking the good along with the bad... no, I know there is no worry about the person you will be down the road, and it won't be bitter or resentful.
Leave your former MIL to herself with her own fears and thoughts.... they are hers, and really have no bearing on the person you really are. She can think anything she wants, but it won't stop you from being you, a very insightful, understanding, caring, wonderful person.... the way she chooses to view life is her choice, and if she snubs you.... it's her loss... not yours.
Yes, it does make a person wonder, I know the memories after view the pictures stuck with me for a long time. For a while, I fought with some of my ideas, but in the end, I was glad I went through those pictures, as I was able to validate (for myself) the truth about the marriage.
Take care of you, God Bless
Love,
Laughing
Jeremiah 29:11 For I know the plans I have for you.........