I've been with my boyfriend for 4 years now. He's currently 16, I'm 18. I'm gay, he's bi. Unfortunately, he's from Britain and I'm from Canada, so we don't get to see each other much, except for holidays. However, we've been in contact pretty much every day for the past four years.

Over the past two years, he's had 'sexual relationships' with four different girls during times when we won't be together for an extended period of time. Basically, he goes out with them for sex and then dumps them once he's had his fill. At first, I was really pissed about it, but the fact he told me about it before hand and tried to get my approval took off some of the edge.
He always explains to me that I'm the one he truly loves and that he wants to spend the rest of his life with me, etc etc, but he has sexual needs because he's so young and whatnot; not being there, obviously I can't fulfill them. I kind of understand where he's coming from, I was like that before I started going out with him, though I grew out of it quickly.

Recently, he's picked up his fifth 'girlfriend,' and he's spending the weekend with her right now. Three days I won't get to talk to him. It's been about 5 months since the last time he did this. He asked for my approval and tried to soothe me/make sure I wasn't upset over it before he left. He's been texting me reminders that he loves me every few hours.
Even so, I'm taking it really badly this time. I understand him having sexual needs, but part of me is thinking he's old enough that he should be able to handle them, and that he shouldn't be hurting me like this if he really loves me. I've spent the past two days crying, wondering what makes me so much more special than these girls. I'm even so upset over this that I vomited earlier.
I want to let him know how angry I am with him, but whenever I even begin to do that, he gets really depressed (and breaks down into tears, even). I can't bring myself to make him cry, no matter how much I want to let him know. Because of this, even in the future, I'll have a really hard time trusting that he isn't cheating on me. But I love him too much to do anything that could possibly hurt him.

The obvious answer, even in my mind, is that this is probably an unhealthy relationship, and that I should break up with him. He shouldn't be hurting me like this if he really loves me. But that raises the question, does he really know how much he's hurting me, since I can't bring myself to outwardly tell him just how displeased I am with this?
The problem is that I love him way too much to cause him any pain.

Any tips on how we I could possibly come to some sort of resolution that doesn't leave either of us in tears?