Stay off of it. Going back on fin will only screw your system up even more. Side effects often resolve within 2 weeks, but it’s different for everyone. It took me 5 months to recover (from 2 doses), some people take years, and some people have yet to recover.
You may be in for quite a roller coaster of ups and downs, so brace yourself for it, and talk to your girlfriend about it instead of trying to hide it from her, it’ll drive you insane otherwise.
The depths of how horrible this condition can be are extremely deep, much worse than simply erectile disfunction. You may simply get lucky and your body recovers in only 2 weeks, but be prepared for it to take even longer.
And to reiterate, do not take any more finasteride. Going back on it won’t return your body to the state it was in while it was still on it. Once your body freaks out with either coming on or coming off the drug (and the crash probably would have come sooner or later even if you stayed on it), your system gets knocked way out of balance and needs time to figure itself out. Taking the drug again will only mix it up even more.
Hope you recover soon.