He has an engagement ring and won't propose why?

More to my question - I have known for about 8-9 months and he does not have a clue that I know. (That he's got an engagement ring) We live together for almost 2 years now and have bought a home together in the past year. We talk of getting married, know the colors, the season, bridesmaids and best men, etc.... Half of the times he will be the one initiating coversation reg. "our wedding" but I am not sure why he won't propose. There has been many opportunities..... HELP! I am starting to think that he has second thoughts....
REPLY:
Is there a date for your wedding?
If yes, then a proposal is superfluous. It's a wedding ring.
If no, the next time you talk about your wedding, ask him when he wants to marry. Make a date.

When you talk about getting married, does it make a dreamy, hypothetical impression? ("What would be the best season.." "If we marry.." "What colors would you chose..")
If so, could he be exploiting you?
You might also want to look at
Why_do_guys_hate_to_commit_when_they_initiated_the_relationship_to_begin_with
and
Why_do_people_need_to_be_married_to_feel_and_be_committed_to_one_another