I read similarities to how I was when I was your age in your post, SarahSweden. I did not marry until I was 39 (met my husband at 34) and was in therapy for mother issues from when I was 29 to when I was 38 (and then 47-56).

What I learned over the years (I'm now going to be 66 next month) is that you cannot want/long for what you have never known. I was a virgin for a long time and would have sex dreams but would always wake up just when it was getting good :-) It wasn't until after I was married that I realized that was because I only had head knowledge of that part of sex? Even having masturbated/had orgasms I had not been with a man so dreaming the situation, I could not fill in those blanks because I had not had that actual experience.

It sounds like you had a "good enough" mother and want the things that felt good about that relationship and, since we're talking conscious imagination, what you can imagine you know feels good. I would look with your therapist at when you have those feelings the strongest; what you are thinking/doing, what is going on around you. My mother died when I was 3 and my stepmother and I were "not a good fit" to put it as my therapist did But I could still long for the comfort of a mother, especially when I was feeling lonely or anxious? It's probably a form of self-soothing (like a thumb in the mouth of a toddler instead of a breast)? Look at when you experience the feelings the strongest? Identify and tackle the actual issue/feeling head on. When you are lonely, make a plan for how to make friends or do something with others or identify an interest to pursue, etc. Maybe volunteer and meet an older woman to mentor you in some way and get out and meet some men and talk to them; one cannot get experience without putting in the time/practice?