<human>: Could you distill the essence of the text into 1-3 sentences?

So my girlfriend and I have been together for about 3 and a half years now, we have our ups and downs like every couple but on the whole we're very happy together.  She also uses reddit but apparently didn't realize I know her username.  I look at her account every once in awhile to see if she posted anything funny or commented on stuff, I don't do it often though as she isn't very active.  Anyways, I decided to check it out the other day and I found a  post she made in the subreddit for depression about how lonely she has been lately.

We're basically each others only friends and spend all of our free time together.  She mentions in her post we make each other happy but ever since she stopped hanging out with her self destructive friends she can get very depressed and lonely.  She also mentions feeling the urge to self harm again which she hasn't done since high school (I was also totally unaware of this).  At this point I don't really know what to do, I want to be supportive and help her but I also recognize this was clearly something private that she didn't expect me to see.  So do I being it up and explain how I found out, or just try to be there the best I can?  I believe in being as honest as possible with the people you love but I don't want to make her feel embarrassed for opening up to who she thought were strangers (she doesn't generally like sharing this kind of thing with me).
<bot>: Girlfriend made a reddit post about wanting to make friends and being depressed, she didn't know I know her username.  Should I bring it up, what is the best way to help her?