You could point out that if his excuse is that your parents, and not you, are paying for the place, maybe he should go find relatives of his own to pay his rent obligations (as initially agreed) so he isn't either. He ought not be expecting your parents to subsidise him.
Ignore any perceived vitriol towards folk being helped out. That's what families do, help those family members in genuine need. (It's a pity it hadn't expanded to include the whole world, but naturally one prioritises "one's own" first.)
I think your boyfriend may well have financial issues, but they seem to be of his own making. He seems in need of a course teaching domestic finance management. He is using you (and your parents) as relief from his situation, but without your permission and against what he agreed. His excuses may seem plausible on the surface but you don't need to look far to realise they are, just excuses.
You may wish to kick him to the kerb, or alternatively agree to support him instead, until you realise he ain't ever going to get himself straight. In any event you need to make a stronger stance and decide what you agree to going forward.
Good luck trying to turn his attitude around. Not looking overly hopful at present, based on what you've posted.