It can be very difficult to be with a mate who "sees the glass half empty" while you are working at manifesting the life you want and maintaining a positive attitude. Just when you feel confident that you're vibrating on a frequency that is brought about by positive thinking, that person that you love and care about falls into his/her normal state of needing to complain about everyone and everything.

The first thing that you have to do in this situation, and what you should do in every situation that involves a person in your life who tends to be negative;don't surrender your power to be conscious of your thoughts and in control of your thinking! Since your ability to think a thought is the single most powerful force in the universe it should be protected without question. If you buy into the rantings of the other person, and you allow your thoughts to follow their lead and take a negative turn, you are freely giving them your power. 

I recommend that you talk to your mate and ask them to respect your need to be free from listening to negative comments or grumbling and that you consider living the most positive life that you can to be paramount to your happiness.However, prior to this conversation be sure to visualize and feel good about it. 

Lastly, keep in mind that regardless of your mates personal view point on the value of living a positive life,  you must remain steadfast in your efforts to stay in a positive place and refuse to participate in negative comments, gossip and grumbling, .