How do I tell my bf?!

I’ve been with my bf for 4 years. During these past 4 years I’ve noticed a lot of things about his family that went unnoticed for a while. One of the main issues I noticed was money. My bf started working a good job last winter and was making good money. His parents didn’t really work...they would buy cars from auctions and than sell them to others. They never really made a lot of money off of doing this. Long story short, my bf’s dad convinced my bf to invest in their car business, quit his job, and basically give them over a thousand dollars to go buy a car so they can “sell it for them”. Months after things got so bad that his parents had to sell all the cars they had, even my bf’s car he invested in, so they could pay for their rent and etc. After that, his parents would keep asking my bf for money even though he had a part time job. They didn’t have a job for months & kept relying on him. Finally his dad found a good paying job and has been working there for about a month now and his mom just sits on the couch all day. Even though his dad has a full time job and my bf is currently out of a job, they will still come up to my bf and ask him for gas money, rent money, grocery money, etc. Last week his dog got sick & they took him to the vet. His parents “couldn’t pay for it” and asked my bf to pay for it, which was about $500. Now my bf’s account is basically drained because of them. His parents owe him thousands of dollars but I know they won’t give it back to him for a while, if at all. It sucks because I know that my bf was saving his money for what he wants and for things that we want. It breaks my heart that they can emotionally manipulate him and he doesn’t even notice. Them draining his account has affected us as well because when I want to go out and do something he’ll decline because he can’t afford it. I’m the one who has to pay for him all the time. I don’t mind because I have the money but it sucks and puts a burden on me as well. I just don’t understand how parents can do this to their child and basically take everything from them. We’re both 21 but live with our parents while we’re trying to save to move out...which is almost impossible now. His dad is making over $90k now and I feel like there is no need whatsoever to keep doing this. I feel like they just pick and choose what they want to pay for themselves. They drink a bottle of alcohol every 2-3 days and smoke at least 2 packs a day so they have money for all this, but not enough money for everything else? His mom is very capable of getting a job as well...she just sits and sleeps all day long. If you’re family is struggling as bad as they make it than why not get a part time job? Idk how to talk to him about this because he never sees this happening. He thinks his parents just need his help...but at this point it’s just too much and it’s heartbreaking to see. How do I even go about this?