<human>: Condense the text into a few key points

I 21f have been dating 28m since May. We are exclusive but it has never been discussed and we do not use bf/gf terminology.  We have amazing sex, we have a lot of fun together, we have never even had a real disagreement but something just doesn't seem right and I want to kind of just give up but I'm not sure why. He'll make comments like, "just because we're being ourselves doesn't mean it's going to work out" and it's not even in a context that really matters but just random reminders that this isn't serious, I guess.

Honestly, I want a serious relationship even if it only last for a few years because that will be a few years I devoted my time to something and I'm not old enough or ready for marriage.  
He ended a 2 year relationship in April and I guess he's just enjoying the fun. He even has said that were just taking it day by day.... 

I enjoy him and his companionship,  but I want to know what the point in dating if you know it isn't going anywhere and if I should quit while I'm ahead. Please help.
<bot>: I don't think we're in the same place, how do you when know to cut your losses and move on?