Hi Grace welcome to the forum Your 18 grace,you have just been given the following advice
You would need a fiancee visa, but you need to be 21
so it looks like your not going to join your boyfriend in the UK for at least 3 years,thats a long time when your 18 if the relationship is as serious as it seems may I suggest you spend the next three years doing a university course,your guy will sponsor you I am sure so when you do eventually arrive here your an asset to him,and you have a degree under your belt Concentrating on your education at your stage in life will take your mind off the 3 years your going to be temporarily seperated,good luck in life