Hello, I am currently dealing with depression myself and have been for over a year. I have been on several types of medication and have been in therapy for several months.
It is important to understand that everyone is affected by depression differently. How it affects you, it may not affect your partner (or the relationship in question)
A part of me feels that, if two people in a relationship suffer from the same condition there is an understanding between the two which can be used in a positive way.
They will know how they themselves want to be supported and thus use this as inspiration to support the other. The two can encourage each other and simply be strong for the other.
However, the difficulty in this is that, if one is progressing while the other is not, what will happen is that one becomes the support while the other, the supported.
He or she will be supporting the other, despite the fact that they too are unwell, which could become very overwhelming and lead to the other becoming more unwell. (It is a possibility, not a fact)
I personally cannot have a relationship at present until I have overcome my personal issues.