Why she became so cold hearted?

She probably feels lost or she's protecting herself (in a sort of building walls up around herself). The relationship she was in, she probably didn't get a whole lot of attention. And when the two of you started talking and doing things together, she probably started to get comfortable and enjoyed the attention from you. She was probably hurt before from a relationship or from someone close to her (I'm guessing or maybe she just doesn't feel comfortable with herself. She's probably insecure at this point). Some girls break things off with guys that they're too comfortable with and fear that they are going to get hurt in the long run. So they distance themselves before they can get hurt.

She probably needs reassurance that you're there for her. Or you will still be there for her, when she's ready to let you back in. But be careful when you get close to her, when she said you were 'smothering' her, she's really telling you to give her some space and let her figure things out for herself.

Good luck. ^_^

Sometimes being straight with a person sucks - so sorry in advance...she's just not into you anymore. When a girl feels smothered she loses her attraction for the guy and that's not something you can just get back. It's either there or it's not. You sound like a great guy. I think the best thing for you to do is leave her alone. Sometimes when a girl realizes that she's pushed a great guy away and he ACTUALLY went away she slowly comes back. Hopefully you've found someone even more awesome by then so it won't even matter.

Good luck.

You're too direct with her. I understand that, I'm pretty direct myself. But what I really think the problem is is that she needs an excuse to hide away...maybe she's found another guy, or just lost interest. Once you give a person your all, they take it and move on. It would've been nice to act a bit mysterious... or teasing perhaps. Anyways, if you don't hear from her, I'd recommend shooting her a text, asking if she wants to talk about what's been up.