She would rather talk to him than me

My girlfriend recently met a guy on some office trip and began chatting with him more often after they returned. She says he’s not like the other men in her workplace and that he really gets her. I wasn’t worried about this earlier because I was happy that she found someone to interact with. Lately, however, she is almost secretive about what they discuss and how often she meets him during office hours. She’s not cheating on me or anything, but I sometimes get the feeling that she would rather talk to him than to me, which is a little troubling. She says he knows of my existence, but I wonder if this is something I should worry about because it seems as if he is trying to get closer to her. What should I do?
If you trust your girlfriend and believe your relationship to be healthy and stable, this shouldn’t be a problem at all. If you don’t feel this way, it shows there are some things you both need to work on, which is what you ought to identify and begin working on. If this colleague bothers you, why not tell your girlfriend how you feel and ask if you can all meet together somewhere? That way you can gauge him for yourself instead of assuming the worst about his intentions. It’s possible that she may want to keep her personal and professional lives separate though, so you should be mindful of that too. Either way, this isn’t something that can’t be sorted out through dialogue, so speak up.

I want to tell my girlfriend to stop complaining as much as she does but can’t do it without making her feel as if she isn’t important. I try my best to empathise, but she is just pessimistic about everything. How do we fix this?
Listening is an act of empathy, even if it feels as if the other person complains a lot. You don’t have to come up with solutions, but cultivating patience is good.