For people 24 and over, how do you cope w/ goodbyes? My boyfriend w/whom I lived for 5 months left yesterday?

I would re think the situation right now. Since, you're still young I wouldn't get any deeper into the relationship. He's definitely sending out some red flags "threatening to break up with you" just because you won't meet his demands. Imagine how you will be in a couple of years. You'll be more likely to listen to all of his demands because you've been together for such a long time. I suggest not ruining your life and find someone better for you that doesn't just demand but some one who gives a little and takes a litte. I hope my advise helps and that you take it, if you don't break up with him than you should have a serious talk about all the issues.