He is radically true, and she is radically false.

A fatal split would have been inevitable.
Nothing could be better for them both--after their momentary outburst of love at the end--than death.
From the point of view of art, Constance is interesting.

It is more than we can say of Domizia in _Luria_.

She is nothing more than a passing study whom Browning uses to voice his theories.

Eulalia in _A Soul's Tragedy_ is also a transient thing, only she is more colourless, more a phantom than Domizia.
By this time, by the year 1846, Browning had found out that he could not write dramas well, or even such dramatic proverbs as _In a Balcony_.