The Mahari'k in shoresh 10' says that the chiuv onah is considered davar she'bemomon meaing a monetary issue.Therefore a person must give all he has got to fulfill it.
We see that when paying a debt the bais din takes away all but a few things.Which tells us that more than a chomesh which is required for an Assay is required of someone looking to pay his debts.Therefore that which shall be an excuse in a regular mitvah shall not be sufficient in a monetary issue.
According to this certainly the husband is obligated to treat his condition.However even according to the shulchan aruch that it not considered monetary which is why he can not make a condition with a wife to be exempt of this obligation according to the shulchan aruch,nevertheless since it is interpersonal it will require him to do his utmost to fulfill it and act on it as though it were monetary.
In conclusion he is obligated to heal himself of this shortcoming for his wife's sake.
In regard to whether or not the husband may rely on the forgiving of his wife and not treat his deficiency,'oror is it a chesed on the wife's part to be forgiving in this area.
The Gemarah in Yevomot 109'b' relay's an episode where Chonyov the son of Shimon Ha'Tsaddik was offered the Kehunah Gedolah after the passing of his father. He declined as respect to his older brother, letting him take it for himself. After a while jealousy took hold of him, which led him to disgrace his brother thereby causing himself to have to run for his life to Egypt and build what became known as Bais Chonyov to serve as his Bais Hamikdash.
The depth in this story is as,cited in that Gemarah,Rav Yehohuah Ben Peracyah said "before i became Nassi i would say that if someone were to push me to accept such a position i shall give him over to the lions,and now after being Nassi if someone should tell me to step off i would spill burning hot water on him".
This meaning, that when giving up an opportunity so tempting as this,one shall be sure that his heart is fully compliant with it.For when the jealousy kicks in later it shall be it shall be in great measures,and will leave you in a state of inconsolable regret.
Now,in our case,do we know that the wife is all forgiving and not suffering in silence? Is she really complacent being robbed of her basic rights?
Therefore i conclude that the husband should not rely on his wife's forgiveness and should undoubtfully treat the condition and give her that which she deserves.