The grief process does apply any time you lose someone, or something, important to you. Your post doesn't make it clear whether he is just going through some doubts right now, or if he has broken off the relationship. We also have a relationships forum, and if you are still trying to work it out, you might try posting there. If this is the end, then you will need to go through a grief process as you would when someone dies, or as you would grieve for the loss of your marriage after a divorce (even when you stay friends, there are changes that need to be grieved).

How are things going now?