I understand this and relate on a few different levels.
First though, re: the OP's question about sex: I feel that sex (or lack of it) has definitely contributed to my depression and mental state regarding CTB. I won't bore everybody with the details, but essentially my situation is that I was diagnosed with a painful reproductive condition in my mid-20s (although I'd been having symptoms since my early teens, just wasn't officially diagnosed til later) that made the act of having sex VERY very painful. I was only with a couple guys before my diagnosis, so really compared to most woman my age at that time, I was rather inexperienced. And the sex I did ever have was miserable because of the pain and also the few guys I'd been with weren't men I was deeply in love with. Then, I had to have a hysterectomy at around 30 yrs of age and after that, I had basically no sex drive due to hormonal changes and also increased depression (already had MDD before my surgery). Last times I tried having sex were awful, and that was around 20 years ago so...a very long time to go without physical intimacy. So I very much wish I'd have experienced amazing sex with someone I loved and had a true, deep connection with - but I never have and I feel angry and sad sometimes that that was denied me in this crappy life.
Which brings me to your comment specifically -- I was with someone a very long time ago who was the only person I ever felt a deep connection with. We had so much in common and there was just this...chemistry with him that I've never found or felt with another person. But this person broke up with me and moved on with his life without a care, while I spent so so long mourning the loss of that relationship, and so hurt that I was nothing to him while he meant so much to me. And the thing is, he and I were young (late teens into early 20s was when we were together) but we never had actual intercourse yet the physical intimacy we did have was more exciting, more special and more meaningful to me than anyone I later had actual sexual intercourse with. I've often wished I could've known what it was like to have experienced that physical connection with him, someone who turned me on physically AND who I was so attracted to mentally.
So I know what it's like to not be able to move on from someone you considered a soulmate, and how no one else ever seems to compare. I'm so sorry you have experienced that as well. I don't know your age but I hope you will finally be able to reach a place of at least less pain in regards to your lost relationship; I am 51 and spent almost 30 years aching so badlyand mentally suffering due to the ending of mine and would never wish that on anybody.
Peace to you. (Also, apologies for how long this post got to be)
Edited to add: I meant to also say that if you ever need someone to talk to or vent to about what you're going through in regards to your lost soulmate, please reach out to me. When things were most painful for me, I found that almost everyone - even my family and so called 'friends' - didn't want to listen or help me while I struggled with my hurt and emotions. So I told myself I would always be there for anybody else in that position. And though I can't really do anything much to help, I can willingly and happily listen and just be there. I'm a good listener.
