Love doesn't need to be shown to us in order to exist within us. It isn't something that is "learned". Love is an emotion. It is a physiological aid to life and attachment. It just is.
Attachment patterns are different to the emotion of love. Attachment patterns are learned ways of a young child getting the best care possible in the circumstances. In my circumstances with two very abusive parents who were not at all loving, I learned to get the least worst care by isolating and being alone. But I also needed to be fed and housed. So there were parts of me that needed to attach to the abusive parental units as well. So my attachment style is largely avoidant, especially for physical and emotional safety, but I attach for the purposes of ensuring the essential needs of life - food, shelter, etc.
But that is separate to love. Love for my alters - especially the hurt little ones - comes from my compassionate adult self that can step back and "knows" the child selves deserved more than that. These are the adult selves that the article you linked talks about. They didn't learn love or compassion from an external model. It just exists in us as it does in all human beings.
Somewhere in you you also have a wise compassionate self. It might be easiest to access it in relation to external others first. Like... to other hurting children. You don't need to have been shown compassion towards yourself in order to know how to feel compassionate towards a hurt kitten, a crying child, a dying animal etc . Unless you are a natural psychopath and have no capacity for empathy with others this compassionate self exists within you also. This is the part of self that needs to be nurtured and developed in order to be able to give it to yourself. And contrary to what you may think, it doesn't need care and compassion shown towards IT before it can feel it alone. It is already there, a natural part of your own humanity.
This is the part of self that can be grown and developed with the support of a therapist. It doesn't need the therapist to give it love and care. It just needs to learn how to use that internal compassion in service of the younger, hurting parts.
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