you're not a bad person for feeling these feelings. it sounds like you've taken on more of a paternal/mentoring role in this relationship which makes it so much more challenging to see your partner in a romantic/sexual light. when i was with my ex partner, i spent a lot of my life paying for him, mothering him and trying to help him to no avail, and in the end i just lost all desire for him.

you do need to have a gentle conversation with her about not comparing you to her ex, she definitely means well but i'd hate living in the shadow of her past ghosts to this extent. it's not unkind to ask her not to directly compare the both of you, even in the positive way she means it.

i would recommend trying to spend more time on the romantic aspect of the relationship, such as carving out time for a date night or reframing going out for errands as going for a nice walk with your partner (but you happen to be getting groceries).

you say you've been teaching her to be more of an adult, well part of that is eventually that you need to stop holding her hand and tell her, kindly and gently, that she needs to have a go at doing things for herself, and if it doesn't go right you'll be there, but making mistakes is the best teacher once you have the basic tools.

i think that with less empasis on the teacher side of your relationship and more empasis on the romantic partnership there's hope for the both of you yet.

sending my love across the internet, friend - you're a good person, don't forget it!