<human>: Can you summarize the given text in a few sentences?

So i met my very first girlfriend and we started dating about 3 months ago. she told me right off the bat that she has mental health issues, mainly extreme anxiety and depression. For the first couple weeks, everything was great, as i assume the the happiness of a new relationship can have this effect.

but now, on and off since then, she has periods where she is completely different. she rarely texts, when we talk on the phone its awkward and forced, and she doesn't want to hang out or even go out, and ends up sleeping most of the day.

at first, i was accepting of this, but now i don't know what to do. as someone who doesn't have mental health issues, its extremely hard for me to empathasize with her being this depressed and distant from me without thinking its something i've done or that she wants to break up. she's like two completely different people.

i still want to be in the relationship, even despite this, but i just don't know how to see things from her point of view and how i can help her. 
basically, im just asking how i can best support someone with these illnesses, and how i can learn about them myself to better understand her. if anyone has or had a partner like this, your insight would be MUCH appreciated.

i think i might need to end things, but i do believe if i understand what she is going through, it will ease my worries and help her with hers.

ive tried talking to her about it, but she always tells me not to worry and that its nothing serious. i just want to know how i can help her without her knowing. how i should treat it and if i should give her space during these times or not.
<bot>: girlfriend has severe anxiety and on and off depression, and i worry about her, and myself, so much that it is affecting me personally. how can i help her? how can i empathize?