My heart is breaking... I thought Christians are suppose to love "unconditionally"

[Wyrd of Gawd]

There are very few xtians who will partner with an atheist.  The xtian belief system teaches that atheists will burn in hell for all eternity.  If your GF believes that, then she would constantly have to try to bring you back into the xtian fold, to save you from her god's eternal judgment for not believing he exists.  If she rejects you for your lack of belief, then it's not going to work.

My personal experience of xtian "unconditional love" is that it only applies to xtians who believe exactly the same things they do.  Everybody else on the planet can burn.

I've never thought of it that way.   I thought love means love and not only to the same believers as you are :/

Consider yourself lucky.  You don't have to go through a divorce and lose most of your stuff.  The longer you whine about her the longer you will be unhappy.  So forget her and move on to someone better.  There are millions available.  So bury the relationship and start looking.

I can understand your advice. I am still lucky to be in this stage now than later. However, she's not one of those who knows the Bible inside out or one that goes out on missions and preach the gospel. She admits she's consider herself not a strong believer yet. That's why I want to hope that she can be one of those wives with non-believer husbands (which they exist, she and I even know a family in our community). This gives me hope. If she can be like that lady, it'll be the greatest solution for me but I need ideas how to get her to be like that.

It's impossible to get anyone to change their minds.  As a case in point you won't change yours so why do you expect her to change hers?  If you frame the situation differently you may see other options that will give you acceptable outcomes.  But your current situation is a dead horse.  It's not going to move.

Realize that even if you do reach an agreement and are able to move forward the original problem will still exist and will never be resolved.  It will always be a source of conflict.

She has clearly stated that this issue is a deal-breaker.  Accept it and find someone else before you get any older.  Millions of other women will accept your religious views without any problem but they will get pissed off about something else that might be easier to deal with.  

Don' have hope that someone will fulfill your fantasy.  Work on fulfilling your fantasy about what you want to be.  You are the only person you can control so make yourself happy with yourself.  You may find someone who will tolerate you if you give up the idea of controlling her.  You aren't letting her control you so stop trying to control her.