<human>: So, today me and my girlfriend were at a LAN. We were gaming, and all of a sudden she went out of the room. I thought she needed a toilet-break or something, but she didn't come back for nearly an hour. She usually takes about ten minutes when she goes to the bathroom, max. I threw away a text, but she didn't reply. 

When she comes back she hardly looks at me, and takes a seat a bit away from the large group of people. I get up and walk over to her. I kindly ask where she's been, and she replies by shrugging her shoulders. Then I gave her a kiss on the cheek. She was cold as ice (from being outside) and she smelled of cigarettes. I just ignored it and went back to the computer. 

I don't really mind her smoking. I know that it can feel good when you're down and stuff. I wouldn't know, I've never tried it. I'm just worried about her, and I'm afraid she's lying to me for some reason. 

I have no clue how to confront her about this, since she's a careful and shy person. She's also suffering from depression. 

*I'm posting from my smart phone, so excuse any mistakes and not tagging the post.

Could you distill the essence of the text into 1-3 sentences?
<bot>: I'm afraid my girlfriend has started smoking cigarettes behind my back. She's shy and depressed. How do I confront her in a kind way?