Relationship Troubles

So I've kind of figured out that my parents don't like my boyfriend. It hasn't always been this way, but back in December something bad happened. I chose to consume marijuana for the first time ever and it caused a manic episode. Instead of immediately calling my psychologist and my parents, my boyfriend gave me benadryl, hoping I would sleep it off. My parents were extremely upset with him for reacting this way, and since then I've had two very emotionally charged conversations (one with Mom, one with Dad) during which they voiced their concerns. Some stuff has happened that has made him not look so good since then. He actually got fired from both his jobs (he has a new job now), and I think he started using more marijuana with a recently reunited friend. My parents are right in some ways: he's sort of been acting like a teenager more than a 25-year-old. But on the other hand, it's a good time for him to get this stuff out of his system. I'm not living with him, he doesn't have any children, it's his first time to really be fully responsible for himself and not have his parents looking over his shoulder. I see it as a time for growth, and making his own personal choices. It's not like he's a slacker. He actually started exercising religiously and lost 40 pounds (and plans to lose more!). He spends time with friends, so he's not totally anti-social. He's doing well at his new job. All of this is more than I can say for myself. I live at home, work in the family businesses (my parents are both self-employed) and can barely function when I'm by myself. It's a very tense time for us, but we've been together for almost 4 years, and I don't want to give everything up just because we've hit some blips in the road. I mean, if I should be breaking up with him, he has every reason to break up with me. I'm mentally ill with no foreseeable direction, taking a ridiculous cocktail of medicines, with no close friends and nothing to really motivate me. I'm just as much of a mess as he is. Someone once told me that we've experienced too much pain and hit too many roadblocks in the relationship for us to overcome such negativity. But I see it as the opposite. If we've come so far, why stop now?

Temper

Here's a good reason to post: my boyfriend has a terrible temper. I always sort of knew this, especially since last year when I saw him fly off the handle. It's scary when he gets angry, he's a big guy and he's strong. I'm not sure if it's getting worse, but he was fired from one of his jobs the other day because he got angry on the job and made it obvious in the presence of one of the bosses. He also has pretty bad road rage, and the other day he got pissed at another driver and made his point by gunning the engine and zooming around curves in a way that wasn't safe. He immediately put his hand on my knee and apologized when he saw I was upset, but still. My instinct has always been to let him have his space to be angry, but I'm a little concerned that the anger is having a detrimental effect on his own well-being and safety, not to mention the well-being and safety of others. The last thing I want to do is be a nag, but if we're going to get married this is something I can't let slide. I can handle it for the most part (except for the driving, I can't handle dying in a car accident) but I don't want my children to have to deal with or witness it. But how do I bring it up without making him angry?