I'd be very upset if my boyfriend bought me a ring he couldn't afford and had to go into debt for. Then again, I'm atypical, in that I don't want a diamond engagement ring because of the issues involving conflict diamonds, the DeBeers cartel keeping the cost of diamonds artificially high, etc. It's a marketing scam that DeBeers came up with in early 1900s to sell diamonds. Which is too bad, cause they are pretty. Ah well.
My 2 cents is that you have no business committing to marriage before you have a job and a house...I think you should wait until you are card carrying members of the real world before you make such committments. It is coldly practical and totally unromantic advice, but you are soliciting loose change . . .