It's going to be ridiculously difficult and you may cry and ask yourself what did you do wrong, but it's life miabosworth. Trust me, I'm going through it right now at this very moment with my ex/gf/whatever of, guess what, 4+ years now. It's been 2 weeks now and I swear that first week was hell, but it has actually gotten a bit easier this week. I haven't seen her in almost 2 weeks, but have been talking to her just up until 2 days ago. I had to officially embrace a NC rule myself. I want her back so very bad, but the reality of the situation is that she's gone. Your boyfriend MAY very well miss you like crazy and want to get back with you next week, but be prepared for the worst and try to put it in your head that he's already gone. I've been trying to take my own advice and it's difficult at best.
I read somewhere yesterday that logic and rationale simply can't be used when a significant other wants to break away because feelings and emotions can't be rationalized and held down my logic. The heart wants what it wants. I tried to talk and talk and talk and talk... and talk things out with my ex to no avail. It got to the point where I was actually doing more harm than good because she would get annoyed and pissed at me for constantly talking about the relationship and telling her how much I loved her. I now realize that it's completely out of my power and I just have to leave her the f*** alone and move on with my life. I'm still holding out hope that after a 2-3 weeks of NC that she'll come running back to me, but the reality of the situation is that our relationship is very well done and over with. It's confusing and doesn't make sense to me, but it is what it is. Keep doing what you're doing, no contact with him, focus on yourself and read a few similar questions on here to get even more advice. Just remember that it could always be MUCH worse, you guys could have been married with kids and it could turn out to be your best friend or sister that he left you for, some real Jerry Springer s*** lol.