Growing as a person is done in relationships, not alone
The opinion everyone seems to have is that no one changes for a significant other, that you can only ameliorate yourself as a person when you are alone and independent. However, I have found that to be a half-truth, at best in real life. People change when spurred to. They grow when they feel safe enough and confident enough. Love provides a safe cover under which to find and fix emotional pain in the way of your happiness. We are built to help others grow, we aren’t meant to pay a therapist as our only means of help. In my life I have completely done away with emotional and physical pain due to childhood trauma and it was mainly with my now husband of 20 years (we married early). I wouldn’t have gone through a metamorphosis of this kind if I didn’t want to be the best person I could be for him, and subsequently for my children. I didn’t have the confidence to be my best self without his stability and his belief in me as a person. I’ve surely helped him through his own struggles, as well.
Edit: in my own experience, my husband helped me make the changes to be a the kind of person I really wanted to be. However, I don’t think that’s the only kind of relationship that is relevant to the conversation here. This could mean any deep or personal relationship where you can’t just run off whenever things get hard.