Depression can make communication more difficult because depression tends to make people more sensitive to criticism and more likely to interpret neutral comments negatively. Depression can also contribute to an increase in topic avoidance. This means that your partner will likely divert the communication by changing the subject or making excuses to talk about it later (but they never bring it up again). Your partner's depression also contributes to their feelings of isolation and eventually leaves you feeling isolated as well. In all of this, the important thing to remember is that neither of you are to blame for these circumstances.
Understanding that depression may be the culprit for the communication problems in your relationship will help you to help your partner get through their depression. It also helps you let go of self-blame or anger towards your partner about the communication problems, and allows you to really deal with the source of the problem. Keep in mind that if your partner is depressed, then their ability to effectively communication becomes impaired. They are not purposely communicating poorly, but rather their poor communication is a reflection of their internal emotional distress. Hopefully this understanding will allow the both of you to find a solution that will treat the true cause of the communication problem and give you something positive to talk about.