Background: I am 23, partner is 21. Been together for 4 years.
We just moved in together a month ago while I am working abroad for a few months, to have a "trial" period of whether we're good together. I have lived on my own for 4 years, he has never lived alone yet.
We are both used to spending all free time inside playing games, but with my experience of living alone I learned responsibility for myself and my health - meaning, even if I enjoy spending time on my PC I still eat healthy, keep my place clean, go for walks everyday, and constantly seek to live a better, happier life. I don't have much of a social life or hobbies yet, but I am constantly seeking ways not to waste myself on the PC.
He is different. He lived with his parents, so he is not used to living alone yet. He plays games, eats pizza and burgers (also has an eating disorder type of thing, where he in his childhood learned to be disgusted by basically anything that isn't white bread, cheese or meat) and just seems to have no care for where his life is going. He says he is insecure about his body and wants to lose weight, but he does nothing to change his diet or to exercise. He says he wants to save money, but keeps ordering takeout which is very expensive where we are living now.
He says he will start taking walks with me, but he's "waiting for the motivation and energy" to do it. As if it would magically come without doing anything?
Simply put, he is quite emotionally immature. Besides his life habits, he is not very emotional, and is not empathetic in the least. In difficult situations, he often makes himself the victim, and gets pissed off if I say things that make me unhappy or try to establish boundaries on what I will and won't do for him (because I don't want to encourage his lazy and childish habits, to become his parent). If I try to talk to him about how his actions are harming him, he gets clearly annoyed and I give up and let him do what he wants.
I love him very much despite everything, and as we are both so similar, I want to support him and help him be happy. I know I cannot live his life for him and I can't force him to change his life if he doesn't want to - I understand that very well.
How could I get him to understand that what he is doing is harmful and not a healthy way to live?