Infantilism is a disorder, not a way of being though it can feel that way. It is usually caused by severe neglect
in a childhood and can be related to reactive attachment disorder; however, the person usually does not have enough symptoms for reactive attachment to be diagnosed with it.
What happens is the child does not get enough attention from their parents or caregivers so they crave it in an extreme way. They grow up without feeling safe and comforted but instead experience feeling powerless, dependency on others and sometimes fearful. So they revert back to childhood emotionally in a "replay" so they can try to get those needs met.
The best way to help yourself is to get treatment as well as talking to others who understand. Here is a forum that might help:
Also therapy can help to provide a way for you to heal through affirmations, self care and relationships with others.
Telling your family and friends is ok to do as long as you feel they would be helpful rather than hurt you with the information. You want to have support, not more problems to deal with. Showing your family information about infantilism can help so they can learn themselves what causes it and why it happens. This resource is about having a relationship with someone with infantilism so it can help your family understand:
There's a baby in my bed!: Learning to live happily with the Adult Baby in your relationship. by Rosalie Bent