What Should I do? =(?

Well This boy really likes me (for almost a year he has) but...i don't like him back. We are really good friends and so he text me saying i found my wife (hes 13). i just played along saying that's nice whats her name? he said mary palmer....i was like ok...then i realized this was true but they are not wife or husband. they are just gf and bf. about 2 days later he said im single now im like you broke up with her? he said yeah...she was horrible she sucks and shes not as good as you....i was like (0_0) i thought she was respectful and nice he said hell no! shes worse then my ex-girlfirend! im like woah 0_0. Then he said we are arguing right now..she started this whole thing! then he said i want you Lauren...you like none of this girls..pretty,nice,intellegent even more. i feel so horrible...cause i dont like him and i keep telling him that. (im not tryin to get into a relationship too young) so what should i say?