I have experience the exact same thing as you. During all my life (or at least as much as I can remember) I have been depressed and suffered from anxiety.
The day I started on opiates was both the best day in my life and the worst day in my life. Immediately I started feeling much happier, I started socializing alot more and I got so many things done each day, where as before many days was spend in my bed because it felt physically impossible to get up. So of course I got addicted to opiates as I finally had a good life. I was happy and I felt i belonged somewhere. Feelings I have never truly experienced before. But after a while by girlfriend said to me that if I didn't stop, she would leave. I have was very fond of here, and I did NOT want to loose her. So I gave her all my stuff and she threw it away (in retrospect I should have lowered by dose slowly, but that is too late now). So I did go through a cold turkey. I felt terrible and it has so far been the worst days (weeks) in my life. But she helped me through it which really helped a lot. I was clean for almost half a year and I experienced some new found joy and I really loved the energy I had. But suddenly things started going wrong. My anxiety got really bad, my depression came back even stronger and I felt that people where stalking me and I felt they wanted to harm me and my girlfriend. So one day I ended up assaulting two men, who I thought wanted to harm us. After that I couldn't get out of bed. I was taking a Master of Science so that started to go bad too as I wasn't doing the things I was supposed to do. In a last desperate attempt I tried getting anti-depressant and phenergan to help with depression and anxiety and to help me sleep. But it didn't work and i started on opiates again. My girlfriend have a father who is an alcoholic and a big brother who is a H-addict, so she couldn't go through this with her boyfriend, which meant that I lost her and this only made things worse.
Today I regret I started again, because this time it is MUCH harder going through the withdrawals. Last time I got my strength from my girlfriend and from the fact that I thought everything would be better after a while. This time I do not have her support and I don't know if things get better after the withdrawal symptoms have gone. So my advice to you: Even though how bad you feel DO NOT start again. If your girlfriend can control it - then give he some opiates and maybe some benzodiazepines and let her give you some at the worst days and then start seeing a psychologist, who hopefully can help you through this. Trust me, you will NOT be able to control the use of opiates and benzos yourself, you will simply fall back in your own routine. That is why I suggest to let your girlfriend control them. Then you can ask her on the worst days if you can get anything, and she will make sure that you dont take too much and don't take it too often. In this way you can get through the worst days and after awhile the psychologist will hopefully start helping you and you are sure not to get addicted as long as your girlfriend are strong enough not to give the things to you too often.
My psychologist said to me that it wasn't exactly an advice that psychologists should give their patients, but some people simply CAN'T live with out help from strong medication until they get what ever it is that are bothering them under control. The trick is not to get addicted to the substances. So some days you can ask here for some meds, and other days she will simply have to drag you out of your deep black hole without giving you any medication.
It will put a big pressure on her, but ask if she is up for it. This is way better than getting addicted to something again - trust me.
I hope you can use this. This is the way I would have wished I took. I regret the day I began again and I would give anything in the world to change that. But it is too late. I hope you don't make the same mistake.