How to end a long distance relationship? Boyfriend moved abroad.

I've been in a relationship with a boy for a year and a half.
We've been really good friends since we were about 12 or 13 and when we were 15, we got together.

The situation between us has recently become rather complicated...
- His parents decided to move from the UK to Malta, taking him with them, therefore uprooting him and damaging our relationship. Putting us into a long distance relationship.
- He is meant to start sixth form there in January, but he will be a whole term behind everyone else, and we both are worried he will have to do an extra year.
- I won't have seen him for about 4 months as his parents won't let him come over until the end of his first term.

I thought we would work as a long distance relationship but it's so hard and because I used to suffer from depression and I live by myself, and I get SO lonely and upset now he's not around.
- Any time I tell him I am unhappy and upset he tells me that he is unhappy too but he can't come back to England because he has to be with his family.
- He always brings up that when we both turn 18 we can get married and be together again.

This is really stressing me out because I feel like I'm too young to be getting so serious, I don't want to marry him just yet! I just want to be single and have fun and just enjoy my life a bit, and if he comes back then maybe we could try again, but right now it's not what I want.

I have told him this, but he always makes me feel very guilty and upset telling me that 'im the only girl he ever wants to be with' and 'itd kill him if I was with someone else.'

I'm gonna be 17 in like 2 days and I don't think I want to be in the relationship anymore.

A further issue also developed a few weeks ago, as we took a 'relationship break' and didn't speak for about a week. I thought it was over and I had a thing with another guy.
My boyfriend then called me apologising and saying he realised that he couldn't let me be with anyone else and when I told him, he cried down the phone for about an hour and at the end said he didn't care because he still wanted to be with me and was willing to forgive me.
This makes me feel so bad as I know he really cares about me but I don't want to be with him any more, but every time I try and end it he makes me feel very guilty.

This is the first proper relationship I've been in and it is just becoming so stressful and a strain on my life. I know that I don't love him any more but he makes me feel so bad for trying to leave and says 'Im breaking his heart' and 'We should try harder as we've been together so long.'

I really really don't know what to do any more, I've tried ending it and I don't wanna end up just cheating on him but I don't want to be in a long distance relationship with him and it makes me feel so confused and unhappy.

Has anyone else been in a situation like this? Please help with any suggestions.

p.s sorry this post is so big :/