Hi, Kate. I'm sorry you're having to go through this. Your ex-boyfriend could be depressed or he could be experiencing a prolonged grief over the illness of his parents - I don't know if anyone could be sure of giving you the correct answer. Keep in mind that even if he sees a doctor, he's probably not going to start feeling better right away. Some of it will depend on the treatment he receives. If he gets medication, he might feel better in 4 - 6 weeks, but again, it may not work. You don't have to be suicidal to have clinical depression. On the other hand, you don't need to put your life on hold while waiting to see if he gets better. You might find a little enlightenment in the book, "I Don't Want to Talk About It" by Terence Real, which explains how depression usually works in men, who generally don't want to admit to any weaknesses. You might consider seeing a therapist yourself for support while you figure out what you want to do. Yes, it's even possible that he just wants to end the relationship, but time will tell. Sometimes guys think they'll feel better with someone new, but you can't escape depression that way.
Maybe try to focus on what YOU want to have happen, what you see in your future. If he should recover, great - then you have a choice to go or stay if that's what he wants, but if that's not what he wants, you still have to live your life. If it's depression, it could happen again down the road. Could you handle it again? Couples therapy is another option, should you get back together.
Hope some of this helped, but let us know if there's anything else we can do. Thanks so much for your question - you're right, you're not alone in this.