Here's the thing. Your guy is really really young. I believe everyone has the potential to change pending their life experiences etc. He still has a lot of life yet to live and I'm not going to say he won't or can't change. Psychics cannot tell us if someone will ever change or not. It's not a fair assumption. However, it really might take a very long time for changes to occur.
Yes, both are the same star signs and unfortunately that particular star sign is prone to selfishness and emotional unavailability as well as very slow progress as far as maturity goes. However, both have the choice to reflect and change some stuff but other stuff is just part of who they are. I wouldn't be able to tell you which part is which though lol. Like my dad was the same star sign as our POIs, but he was super generous, very very loyal, worked his ass off and was never a leech. He wasn't a cheater either. However, his temper was disgusting and he was very abusive and emotionally over the top selfish. My boss is another one that is the same star sign as our POIs, he's married and has been for 20 years, no kids, refuses to get divorced, he's an attorney with his own business, however, he has constant affairs. He says he doesn't love his wife but won't get divorced cause "she might kill herself" but really, it's because he's a divorce attorney and knows she'll take him to the cleaner financially so he's sooooooooo selfish that he will stay married, keep his wife miserable, and just have affairs. He also has expectations in these affairs in that he wants the mistress to be faithful and be emotionally invested all whilst he remains married. His insanity and flawed logic is derived from his over the top selfishness. Selfishness is truly blinding.
I think there's a fine line between NPD and just plain out super selfish. If someone is going out to purposely harm another and just uses the hell out of you purposely and intentionally, then yeah, that's NPD. However, if a person is simply sooooooo selfish and because of their selfishness, they make selfish decisions which causes hurt and pain on others, but it isn't with the direct intent on purposely hurting you to make themselves feel better, then I don't think that's NPD. I think that's more of a "character disorder" and they are just on the extreme end of selfishness. I think that's the case in your case. I also think that's the case with mine. I don't feel intuitively that it's purposeful or intentional, I just think said person is over the top selfish. I've seen another humanitarian side to said person a lot of times. And, I'm sure you've seen a giving nature in yours. Narcs aren't giving in any way, shape, or form.