Should I propose to my girlfriend? lady's and gents please help?

I love my girlfriend to bits she just turned 20 and I just turned 18, but we have been dating for 2 years and like 5 months. we are close to being on our third year. I am planning on saving up for her engagement ring....if i decide to propose, we are so close to each others, we have even caught ourselves reading each others minds. This question has been driveing me up the wall latley, i want to but at the same time dont know if i should. i can not afford a ring but would need the ring before i can propose?