Say, anti-anxiety meds if it's determined that you've got an anxiety thing going. Also, not that this is a common treatment protocol or anything, but I read one abstract where oxytocin, my favorite molecule and the hormone implicated not only in mother-infant bonding and human orgasm but mammalian pair-bonding and (this may be key here) our ability to trust each other, was successfully used to treat male anorgasmia. Yay, oxytocin!
Or then again, (2) it isn't performance anxiety so much as it's the result of initially practical but ultimately unhelpful masturbation habits you trained yourself to respond to a very specific sort of stimulation. Since none of these other acts or orifices except the Fleshlight approximate what you're used to, none of them are working. If it's that, you have to retrain, and it will take a while, but women do it all the time and you can too.
My last suggestion, and please don't quote me on this: Your boyfriend needs lessons.