Sadness when attachment decreases

Please be kind. This is something I'm really struggling with as time goes on. My 15 m.o has always been a mummy's girl but I worry about how mums that are super close to their little ones go when their child naturally wants them less and less. I know it's a natural, normal thing to happen but i am beside myself with sadness thinking about not being the centre of my daughters life anymore. I don't know how I will cope. I have never felt this kind of love before and to lose my closeness with my child who holds my whole heart, the idea feels unbearable. Its something I've not admitted to anyone because i worry I'm the only one who feels this. My husband has been mentally abusive since having our daughter and I feel I've lost him too. I am.also scared of having another child for the same reason. The pain is so great. How do people cope? I suffer from anxiety and low self esteem and wonder if that has something to do with it. My daughter has started pushing away from me when she's upset lately but then wanting me straight back and it breaks my heart.