How To Tell My Boyfriend That This Isn’t Right?

My boyfriend has been working as an architectural drafter for a small building company for about 7 months now, and I have tried telling him that his boss isn’t treating him right but he just won’t listen to me and I don’t know what to do anymore.
He is currently the only drafter at the business – a girl was hired the day after he was, but after being there a week she decided she only wanted to work part time (even though the ad clearly stated it was a full time position) so the boss told her it was full time or no time and she quit. Then about a month later another drafter was hired, but he quit just before Christmas after several warnings from the boss about his work (he was doing a sloppy job and wasn’t completing work on time). My boyfriend’s boss has yet to place another ad for a second drafter, meaning that my boyfriend has been doing the work of 2 people for the past 2 months.
The business had a receptionist/sales rep who was fired just after Christmas because he would continuously call in sick and take annual leave (to the point where he was taking leave without pay) and was just completely unreliable. My boyfriend’s boss has also not placed an ad for this position and has told my boyfriend he needs to handle the phones and sales calls until he does. So, this means my boyfriend is doing the job of 3 people.
Because of his massive workload, my boyfriend generally starts work early (anywhere between 8 and 8:30am when he is supposed to start at 9am), works through his lunch break, and stays back late (anywhere between 6 and 6:30pm when he is supposed to finish at 5:30pm). And his boss does not pay him for any of this overtime. His boss also schedules meetings with clients and my boyfriend to begin at 5:30pm (when the office is supposed to close) and will not pay my boyfriend for the time he is in these meetings working with clients.
I think that this is so wrong! And I don’t understand how my boyfriend can think that there is nothing wrong with this scenario whatsoever! On average, he does an extra 6 or 7 hours of work a week that he is not paid for (almost a whole day’s worth)! How do I get him to understand that what his boss is doing isn’t right?