There's a difference between a relationships failing because you both grew apart and ultimately want different things and then there's failure because you keep choosing the same type of partner that isn't for you.
And no, if someone can't be alone then that means they have self-esteem and self-confidence issues ie insecure. They aren't "secure" within themselves to be alone. It doesn't take strength to go from person to person while not acknowledging your past traumas and hurts from previous relationships.
Hypothetical situation...
You just ended a 3 year relationship to a woman you thought you were gonna marry.
As soon as word hits the streets that you're single, every woman you know is trying to get at you.
They're offering to take you out.
Suck your dikk.
Buy you shyt.
Take you on vacations.
You telling me that you're gonna pass that up so you can sit at home and watch Netflix and "work on yourself"?
Of course you aren't. You're gonna keep living your life and experiencing shyt, and that means other people.
Breakups for women are different than breakups for men.
As soon as a woman is single, there are dozens of suitors lined up to get at her. She can choose between being bored or being entertained and potentially finding a new mate. It has nothing to do with being weak, insecure, or lacking confidence.