This isn't a conversation you can have without upsetting him but that's fine, you're not responsible for his emotions and you're entitled to express your feelings. YANBU to want more from life and this relationship.
My opinion is don't put your life on hold for this loser any more than you already have done, look for someone who is in a situation to actually have a relationship - this guy isn't. Sometimes it happens that way, right person but wrong timing.
I don't know what's led to him being in debt, maybe it's his fault and maybe it isn't, but it's not your fault either and it is definitely his responsibility to sort out.
Perhaps he needs to go bankrupt? If he's living beyond his means he also needs a lifestyle overhaul to ensure that stops otherwise he'll be back in the same situation in no time. Maybe he needs to get help with budgeting, there's lots of debt charities can help with this. Maybe he needs to return to being a student to raise his earning potential, he could investigate the financial possiblity of that with colleges/university and the bank. Maybe he needs to increase his hours/change company or indistry/go for promotion.
Working 7 days a week isn't sustainable but neither is living off someone else ie you. Can he take annual leave one day per week and do the Sundays for his friend? Effectively you're paying his debts for him at the moment, if he was contributing at home he wouldn't be able to pay these debts.
I don't know how old you both are but he sounds early 20s and a disaster zone, someone who hasn't really grown up yet and learned how to be an adult. Then there's you sounding like you're early 30s been carrying him forever and fed up, ready for marriage and DC. I suspect he's older than he sounds and should have got his life together by now. It's a big red flag for your future happiness that he hasnt.
Live separately and stay friends if you want, go out sometimes when he can afford to contribute, but don't date only him, give yourself the opportunity of a proper solid future with someone who's sorted.