A quick poem for you by a chap called Atticus who I follow on insta ...
We've moved on now but if I'm honest I am still a little bit in love with all the ways we were
I think the waves will always come back. The chocolates the kids brought back for me from their holiday with H was a box of chocolate kisses. My ex (the one I was engaged to before H) used to bring me back chocolate kisses whenever he went to the states even after we split up and he would come back to the UK for business (about once a year). He did this for years. When D10 gave me the kisses I had to stop myself from saying "Thank you. I love these. Uncle X" used to bring these back for mummy". A sudden wave of nostalgia, maybe even regret hit me for a split second and stayed for a bit. I think if you can look back without anger or resentment, then nostalgia/sentimentality is OK.
Go get that degree. If there was ever a person who should be engaged in academia, it is you.
I know you work in IT, but may I suggest doing something in the socialogy/psychogy/counselling area. I think you have much too much compassion and a natural gift for healing to waste on computers.