First of all, I was a lot like you when it came to ERPing and such. Not necessarily sad, but just wanting certain things from ERPing without all the bullshit.
The more you look for it, the less likely you are going to find it. It's weird how life works. If a person happens to catch your fancy then go for it but going on the prowl for ERP is just going to be a tiring for you.
We all get lonely and feel like shit but I don't think you should let it go that far. Yeah people are going to treat you as means to an end and really nothing more, which fucking sucks but that's why I think you need to ERP in moderation, too much can really fuck with your life and sense of values. If you get someone, great! If you get rejected, it sucks but going nuclear over it won't make it any better. This coming from a user who just got rejected from something that could have been fun, but shh.
If possible learn some new skills or go for a walk if able, depending on where you live of course. A good walk can do a lot of good for someone who might not know they are in desperate need of one.
And don't think of it as being lonely, think of it as enjoying your own company and being able to reflect on past and possibly future decisions.
And for the girlfriend part, ERPing is not the best place to find a significant other. Probably the worst, I know from repeated experience. They are kind of overrated anyways and having one isn't all beautiful sunshine and happy good times. Just keep that in mind. You and her are both bringing both short comings into a relationship and that is rough. Things get amplified and it's not pretty, but that doesn't mean you should give up if things go south once. But now I am rambling so whatever.
TL;DR go do something with your body