My boyfriend might be using me?

So here's the story,

I went to the Philippines this year for a vacation and my mum got married, during my time there I met a guy, hes 18 and I'm 15 I don't think there's anything wrong with that, I really liked him when I was there and secretly he liked me too, he told me one day he like me when he went swimming with my family. We started spending time together and I fell in love with him, then we started dating.

He would come by the house all the time to see me and all that stuff... but I had to go back to Australia, we talked about it and long distance relationships. I can handle it, after a while... he said he wants to marry me when I'm 18! and he would be 21 or something, he really wants to marry me.. and I'm not sure about it.

I have heard stories that people from other countries like the Philippines use people to come to a better country because the Philippines is poor etc etc.. I think my boyfriend is just using me to come to Australia for a better life, I understand that. Because he's kinda poor himself, he asked for money once too, but I know he loves me but I'm worried that if he comes to Australia and finds another girl and leave me...

I don't know what to do! Does anyone have good advice?

Thanks!