<human>: Good evening, reddit. First time posting, so I hope I do my situation justice.

I have recently entered into a relationship with a girl who I have been friends with for the past four months. I knew she struggled with severe depression before dating her, but now that we are in a more emotionally and physically intimate context, I'm finding her 'down' periods to have a very strong negative impact on me. When her dark times come, she tends to withdraw, act indifferently to all communication, activities, and contact.

I am no stranger to dating individuals with emotional disorders. I've dated a bi-polar schizophrenic for a year and a half, and another girl with equally severe depression for four months. These individuals however, reacted more often than not with anger rather than withdrawing when things got bad. Thus, over the years I have adopted a personal defensive mechanism of becoming emotionally detached whenever I feel a mood swing approaching from my partner, so as not to take the behavior personally. 

My problem is this, I do care about my current girlfriend very much, but I'm so tired of having to stonewall my emotions. I don't want to feel like I'm helpless and powerless in my own relationship when my partner decides to explode/withdraw. When my current girlfriend withdraws, it is as if I'm watching her from outside a bubble, where I'm unable to do anything to show her I care, and that I support her. I feel my words of love and support go completely unrecognized, and that I simply have to wait out the downs. In this process, I feel myself grow emotionally cold and distant as frustrations build. 

I know depression isn't something one can control, and it certainly isn't something one wants to have. That being said, being at the mercy of these swings that can interrupt our plans and days together, and simply wrecks my feelings of meaningful contribution to our relationship. I have talked to her about this, and she says that she'll attempt to communicate more about her thoughts, rather than withdraw when the down periods come, but that her depression has always played a significant and detrimental role in her previous relationships.

Does anyone out there have experience in a similar situation that they have successfully navigated?

Summarize the given text in a few sentences.
<bot>: I very much like my girlfriend who suffers from major depressive episodes, but being repeatedly emotionally shut out by her makes me feel powerless and emotionally detached.