Really could use some advise about my "relationship" please?

So...I have known this girl for about 2 years now. We became really good friends over time, and one day she said she loved me. That was nice and everything was ok, then we had sex. After this she kinda pulled away from me. Now, more or less, she comes to hangout with me because i'll buy her anything she wants, and we do stuff at my house she cant do anywhere else. Well, we talk about everything with each other and she knows I really love her. She has told me though that im a good friend but thats all i'll ever be. When i asked why she said "you just not my type". Well, about a month ago after walking her home one night we hugged like normal i kissed her on the check and said i love you. She answered "thats nice" and went inside and shut the door. That broke my heart. Since then she has been asking for more and more from me (im actually going broke) and i told her i cant keep doing this. She asked, cant keep doing what? So....another month down the road and im where i am now and need some advise please. So...last night she came over to hangout like normal and my cuzin was here. HE knows how i feel about her but was all over her all night and watching her flirt with him and him being all grabby i couldnt take it. I said something to him and he said, well maybe we just wont do it while your around but im gonna **** her. I almost stabbed him in the neck (i just happen to have a knife in my hand). I left for about 2 hours and come back and everyone is drunk and having a good time....everyone but me. So i go sit in my room...she comes in and hungs me and says, i love you, your a good friend. I told her i cant do this anymore and she said whatever and went back out to the couch to curl up with my cuzin. So.....i really love her and care for her, and cant take the emotional stress anymore. I sat in my room crying and thinking most of the day today while my cuzin just keeps asking my why im mad and him and if i hate him. I simply said she ISNT a piece of ***!! So....i really dont know what to do here. Any advise plz? I can give more details if needed, but i think i got most of it explained. Also, i'm 27 and shes 18 if that helps any. Thanks