Hi, this is my first post on this website. I normally don't register to ask questions like this but I am so torn and wanted to get as much advises as possible. My situation is a bit different from other questions I've read so I decided to post my own.
I have been in a relationship with my girlfriend for 3 and 1/2 years. We dated each other about 10 years ago then we broke up, and about 4 years ago we started talking again then eventually started dating again.
We had a pretty healthy relationship, up until about a year ago. I found out that my mom was diagnosed with cancer, which immediately put into a some sort depression phase. So pretty much for about a year, I wasn't able to give my girlfriend the type of attention I used to give her. She used to be pretty introverted and always so dependent on me but recently she got a new job with lots of interactions with people then suddenly she started to become more outgoing. Then I find out that her new coworkers are all guys, they went out a few times and I wasn't happy but didn't think much of it. Until 2 weeks ago she asks me "are you happy with our relationship", I said "I think the relationship could be better but it's not bad" (pretty bad answer... ). Then she talks on and on and finally she says "I love you but I'm not in love with you anymore". It crushed me pretty badly. Then she goes on to say whether I think we can "fix" this relationship, I said "yes". She goes off to the bathroom then comes back and says "I kind of like this guy at work and he likes me too". I kind of expected this but still crushed me even more. I asked her "why are you telling me this?" the reason I asked is because the first thought that came into mind was "is she trying to get me to say f**k it, let's break up". But then she tells me "if we were to try and make this work, I felt like I needed to tell you everything". So far I have found out that the guy kissed her on her head, and she kissed him on his cheek. Also, according to her friend, she felt like she was breaking up with someone when I told her she can't talk to him anymore if we were to make this work. So that night, we agreed to make it work. Then couple of days later, she tells me I need to try harder and that she's sick of trying (from 1 year of me ignoring her) so she won't try.
Now, we are at this weird stage where I try to give her more attention. We try to be out of our house more. We do still talk about marriage (we are dating with the intention of getting married). When I give her a kiss, she doesn't push me away most of the times. When I hold her hand, she doesn't refuse. We have planned and bought tickets for upcoming events out of state. Where the hell do I stand? I'm so confused, is this going to work or am I setting myself up for a bigger heartbreak?
A little bit of our background, we live together. We are under our lease for another 4 months and we have joint credit cards with two dogs.

Thank you and sorry for the long post.

This isn't an easy one, it will not work while she works at a place where she likes this guy. She will see him more then she sees you and it will end. Its hard but you will start to beat yourself up over her going to work. The only way this will work is if she leaves there and I don't really think its fair to give her that option even though she sounds very selfish already saying she likes someone else. If I was you I would let go and try and move on.

If her heart is not with you and with someone else there is nothing you can really do. You can not make someone love you.

I agree with cjk888. In a relationship and situation like that, its not fair that your doing your part to give her more attention while she is not. As long as she works there, there is a big chance that she might fall out of love with you and start to date that guy esp he likes her too. Just think about it, of her saying that she's sick about it from 1 year of you ignoring her. That's s bull reason because she should understand that your mom was diagnosed to cancer so she should expect that some things will change. She only telling you that reason because she's confused of her feelings with another guy.
Man, be strong & don't let her see that your that weak bcause at some point when she see that your depressed of her she would think that you won't leave her because you love her that much so she still keep doing things that you don't like.
Be straight to her tell her that if she really loves you and to respect your relationship she wouldn't let that guy to flirt with her.

Thank you for all of your input, she is actually in the process of looking for another job. She has already told the guy she can't do this because we are trying to work things out (although I'm pretty sure that'll not stop him from flirting with her). The only reason I decided to give this another chance is that she told me about this before I found out on my own. She did tell me that she made it "obvious" that she was talking to some person and isolating... I think it was more of a "pay a F**King attention to me" though... I could be wrong. Initially, I thought she told me because she wanted to break up but she could have just said she wanted to break up anyway. I don't know, that last part is the most confusing part to me. Did she tell me about the other guy out of guilt/wanting me to break up with her first, or does she genuinely want to work things out?

I think she was being honest and the fact that she has almost fallen for this guy shows there is a lack in your relationship. I think you two should take a break. She has become more outgoing and is discovering herself. Give her the freedom to do so. If you two are meant to be, you both will find your way back.