Congrats on the new addition to the family

I understand a little what you are saying. I tend to get very weepy when people are nice to me. It can be something as simple as co workers getting me a birthday cake and singing to me - I want to cry. Because people who have no obligation to be more than polite did something nice. People who were obligated to love me, take care of me, provide for me, support me, did not do so. So nice things can make me weepy, because I have conflicting feelings about being happy at the present, but sad it's not my mom or dad doing it. I have been NC with Dad since he kicked me out at 19 and tried to defame me so no one would help me out (and later stalked me), and Mom off an on since I was 15, the most recent we've spoken was about 6 years ago. She steals my identity when we talk regularly. Somehow NC stops her form doing it.
I am getting married for the first time ever in (hopefully) a year. We are planning to elope to a resort, and not even try to invite anyone, partly because of the cost, partly because his family have become shut-ins and that's its own batch of trouble, but also because it'll be easier to deal with no having my mother there to help me get ready, or share the day. The only women I know whose mothers were not at their weddings had lost them to death. Mine, I'd want a restraining order for bother her AND dad. No generational photos, no mother-daughter moments, and I know I am in my late 30s and not a young girl fresh starting her life, but I still mourn not having stuff like that to have in my life.
I spent part of my 30th birthday party, organized by very good friends and my now FI, in the bathroom, crying, because none of my biological family was present or remembered. One friend found me, and told me THEY were my family, not the people with shared DNA.
It's ok to be melancholy with what you've had in your life. And you know that new baby is in a good place to start his.