“We met a few months ago. We work in the same company. We like spending time together, although we are very different characters, I am very energetic, I love the buzz; having fun, while my boyfriend is secretive, shy, probably zakompleksiony. I bind us with plans for a common future, but my partner says, that a relationship with someone like him would surely make me unhappy. How to convince him, that I dream of being his babysitter?”
I do not understand, why young, healthy man, who lives an independent life, would need care? It looks like it, that this is how you perceive him and that you are ready (regardless of it, whether the partner will accept such a situation) enter into the role of "sister of mercy”. Is it supposed to be a form of support and appreciation of the partner?, who does not believe in his own strength? If that's what it looks like, I am not surprised, that the boy has complexes. Perhaps he needs professional therapeutic help more than your volunteer work? Or maybe he just needs a girlfriend-mate, and not even the most perfect babysitter, who is trying to take over the role of parents?
I also can't rule out, that it's your behavior, the pace of development of the relationship so intimidated and frightened the boy. So I advise you to admit your own mistakes, rethink them and change tactics. Until it's still not too late.