Is it me or her?

I have been going out with my girlfriend for about a year and a half now. We recently moved in together after about 9 months of doing the long distance thing. I go to university, but we met where I grew up. In the past 6 months she has taken 6 overdoses of prescription medication and had 3 trips to the hospital. They have been more serious every single time. I'm not sure what the problem is, but I feel a constant sadness now and I can't figure out if it's other things in my life or our relationship that is the problem. Sex is an issue because I have PE. I understand that sex is a really important part of a relationship, and I do enjoy it. Things have definitely gotten 'stale' in the bedroom though, we tend to do the exact same thing with the lights off. This makes it hard for me, but again, I can't decide if it's because of that or just my feelings towards her.

A usual night:

Earlier tonight we were hanging out like usual when I got a call from my best friend. She disappeared during my conversation so when it was over I went to see what she was doing. She had gone to bed and wanted to sleep so I gave her a hug and a kiss and let her get some sleep. I came to my computer and within 10 minutes she texted me saying 'Prick'.

I'm not really sure what I'm asking. I just want to understand why I'm so fucking sad all the time. There is so much more to this, I'm having a really hard time putting it into words. I think I have a lot of anxiety issues which means I don't have a lot of friends. I tend to sit in our flat most of the day which means I'm a pent up mess of frustration when she comes home. Anyway, things are definitely not what they used to be.

I am recently 20 years old (which to me is kind of scary) and my girlfriend is 22.

Does anyone here have similar issues?