Is it possible to get second master while I already have one? I am in a difficult situation and I am looking for some guidance. I have done my research and I have come to the conclusion that it is best for my mental health to take master and leave. Unfortunately, I already have a master's degree (in another field) and I am a 4th year PhD student and have only one year left to complete my PhD. Also, I am the first PhD student of my adviser. I realize that, I am extremely close to finishing and will probably be encouraged to continue. However, my mental health has been declining over the past several years. 

Earlier this year my dog (who was everything to me) passed away from cancer and I never really had a chance to grieve and have been continuously working since then. His passing caused me to spiral into a much deeper depression than I was in before and in the past several weeks, I have been had episodes of de-personalization, where I have a memory of something that I have done in the past but I was proud of that. But, then that memory is not mine anymore. It seems it's a different person. I know this is related to the stress that I have been accumulating over the past few months and it is getting worse now. The only thing that alleviates my depression is that the thought of leaving academia and this town to move on with my life. I can honestly say that after finally deciding that getting master degree and leave out, is what I want to do now and I haven't been happier in years. Even though, it isn't finalized I think this is a good indication that I am making the right decision.

I have also realized that I don't want or need a PhD to get a job that I want. I really just want to go into forestry or be a greenhouse manager. I am burnt out, unhappy, unmotivated, and uninterested with my research because I can't get anything to work and don't expect to be able to complete my research in the next year. The main reason I feel I'm in grad school at this point is that I feel like I would disappoint my adviser. I know that's not a good reason to stay, especially since staying might be more detrimental for her chances for tenure than just finding another student to replace me on my project. I have decided to tell her that I am thinking about getting master degree and leave tomorrow to gauge her reaction. I need to have her approval before I do leave because I have been her student for 6 years now and need her reference. So if she is not on board with my plan to getting master degree and leave out, then I think I have to stay, but I know my work will suffer a lot in the next year and I doubt my ability to finish my research on time.

What I am wondering is whether or not I am justified in wanting to getting master degree and leave out, if it is bad to have two masters degrees? Will I still be able to find a job if I leave with a second masters?
Your own health is more important than any degree. You should attend to that. If you can do both, perhaps working with a therapist while deemphasizing your degree work for a while, then that might be an option. Stress and depression are very serious. 

Your advisor seems to be invested in you, so you may have an option of a pause or a slower rate of progress. But a second masters won't impede your current goals so it doesn't sound (from here - which is far away) as a poor option. 

However, if you can find a therapist who can help you with the health issues, he or she would be a better source of advice on your future plans than anything you will get here. In fact you may get advice of a complete different sort that neither you, your advisor, nor the community here could think of. 

But for the direct question, I can't think of any downside to having more than one master's degree.