Hi Benevolentbutterfly and welcome to our community
Thank you for sharing your story. It isn't easy is it? Nostalgia is interesting and there is much written about it. What you are experiencing is normal. There are many of us who have the same experiences.
The reason why we experience it may differ though. It could be from good memories or bad memories from the past, or it could be from the present and what's happening now and therefore we miss (feel nostalgic) for the past.
For me it's okay to feel nostaglic about things. It means I have had some very good connections in my life - some real positives. Nostalgia becomes a problem for me when it turns to anxiety and depression. These are things I work on - like visit my doctor and get a referral to a health professional.
Do you see anyone about how you feel? For example your gp or health professional?
Talking helps a lot too. Is there a close trusted friend or family member you can talk to?
You're not alone benevolentbutterfly. Keep reaching out if and when you want to.