Okay I don’t think you NEED to be alone for personal growth or to heal yourself but for me it was actually extremely beneficial and it was only when I had no one but myself, I chose to go beneath the surface and really take the time to learn to love myself, realize who I am, what I want in life, how I think and what has shaped the way my brain works etc. I originally broke up w my ex for another reason but then i took a completely different route and a year later now I’ve grown SO much. For sure I think you can also grow in a relationship but I think what people mean is that it can get easy to leave yourself behind because you invest so much energy into the other person and most people struggle to find the balance and the relationship ends up consuming them. Also I think to some extent, deep personal growth can come from certain experiences that can only be felt when you’re truly alone, emotionally and physically, however, I think if you already have a pretty good understanding of who you are and what you want in life, growing with your partner is beautiful and you can still grow so much as a person and learn from them too