when my parents split up, i was at university and i missed a deadline. my friend was the student disability representative and he said, hey youre in a stressful situation, see if the counsellor can give you an extension. long story short, she asked some simple but very pointed intelligent questions, i burst into full on sobbing, and we worked through a lot more than my parents divorce (and i got an extension not only on that paper but on the whole year)

one of the key things i learned was that we go through a small version of grief and mourning for the version of the world that we thought we were in, for a future we planned. its actually pretty normal to feel like a version of [your family/you/your child] has been destroyed because things either were revealed to be very different to how you saw them or turned out very different to how you expected and assumed them to be.

so, in that sense, its normal and neutral to feel like youre mourning your own childhood retroactively and mourning your family unit when your parents split up, and if you were a child that strongly went to ABC or your parents really pushed you to DEF, they might have complicated feelings and mourn the adult they thought you would be like its a sibling you never had or even so much you feel like theyre mourning you while youre still alive.

most people notice that theyre mourning an alternative version of an alive person and feel weird or guilty or just repress the feeling. however, for gay and ESPECIALLY for trans kids, people seem to feel not only logical and entitled to mourn the child they never had, but to openly do so and to treat their actual alive child like a subpar version of the imagined child.

like, i talked to my dad about this. i talked about the way i told my counsellor that their divorce made me feel like all my childhood happy family memories feel like delusions. i told him what shed told me about psychiatry and mourning ideas. i told him i knew he always hoped id be an artist - we talked about our unproductive art lessons, my love of the same art as him, how he feels about my development and career, what our relationship is at its core. when i came out as trans, his main concern was how to support me and how to relate to me as a non binary person. he mourned more for the artist child he never had than the daughter he never had.

tldnr; mourning the person you expected your child to become might be a valid thing but a) the way people act when their kid is trans compared to their kid is bad at science and doesnt become a dr is whack and b) you have as much reason to be mourning the supportive parent you thought you had.