Listen man, I'm really no expert on porn-induced sexual dysfunction as I've mostly just discovered this and concluded I was suffering from it, but I think there are a few things worth commenting on here.
First of all, limp dick or not, you were headed for disaster anyway. The first thing I noticed is you saying the girl was explicit about wanting a FWB while you wanted a relationship, and now you're heartbroken. The problem is you refused to see reality: this wasn't going to be a relationship, and you were banking on a fantasy. Proof of the mistake is that you're heartbroken over someone who basically told you from the get go you shouldn't get attached. That's not a porn or penis problem, that's a mind and self-esteem problem.
I think you're probably going to have a hard time getting through that on your own. You seem to be in pretty deep waters at this point and one thing to note is that addictions, while they feed on themselves, they're usually caused by something else. You say you started masturbating like crazy around 12. Well, ... most likely, everyone did jerk off like crazy around 12. The problem probably isn't that you're masturbating. It's that something has pushed you to masturbate at an unhealthy rate.
Basically, what I'm getting at is that you should probably seek psychological help. Because your porn/jerk off addiction is more than likely rooted in something else that you've unconsciously been trying to fix or escape from by using. Without tackling this problem, you'll be fighting an uphill battle. Get yourself a sexologist, and while it may be tempting to get a woman, I would strongly advise that you get a man (at least for me, I felt better with the idea of confiding and opening up with a woman, but quickly realized I wasn't as comfortable talking about the darker aspects of the porn I'd watched with her).
I know many here would disagree with this, but personally I remain unconvinced that eliminating masturbation altogether is necessarily beneficial. But I think you'll need to change how you do it. No more porn, and try using lighter stimulation, even if that means failing to cum sometimes. The more I read about it these days the more it seems that what matters above all is to re-educate yourself to be aroused by normal intercourse. Focus on things you'd do with the girl, not on porn-like scenes, and don't stimulate yourself to a degree that will never happen during sex. Also, probably limit yourself. Maybe try to do it only when you're fully "restocked" (sperm regenerates in about 48-72 hours). Being locked and loaded will probably make it easier to get turned on and then cum.
That's all I can say for now. I've long read about how watching porn could make you disconnected from your own experience as it externalizes the mental processes that drive sexual desire. Guess is you want to get that back. You want to own the tools of your own horniness. At least for me, this first step (eliminating porn completely, and jerking off only to my own fantasy), happened quite fast. A few weeks, and I went from having been virtually incapable of jerking off (and often even getting hard) without porn, to being able to do it reliably and rather quickly.
I think you've made clear that this is in your head now: you can easily get hard when you see porn, proving that the problem is not physical. Keep hope. I've known guys who were incapable of staying hard with a girl. A few of my female friends told me these stories at the time. They would be with a guy who just couldn't get it hard. Even though they were young and healthy. It was the stress and fear and all of it. The stories consistently ended the same way: once it went well once or twice, the problem disappeared. Might not happen so magically with you, but it's a very real possibility. Find a girl from whom you feel no pressure, and with whom you feel good and safe.