Instead of interpreting ‘may i feel said he’ as describing the gradual unfolding of a relationship, I think it works better to read it as the dialogue of two lovers engaged in sexual intercourse, moving from caress in the first stanza to orgasm in the last.
As for the parentheses, Tartakovsky divides the uses of parentheses in Cummings’ poems into seven categories: 1. iconicity; 2. protection and intimacy; 3. direct address; 4. layers and frames; 5. interpolation; 6. subversion; and 7. simultaneity. In the first category,
Cummings explored iconicity in many aspects of language, and when dealing with his use of parentheses the most rudimentary examples are those that draw on its graphic shape.
Roi Tartakovsky (2009). ‘E. E. Cummings’s Parentheses: Punctuation as Poetic Device’. Style 43:2, p. 219.
and in the second,
parentheses through their delineation of a separate space also create intimacy. Their protective capabilities and their understated status allow for something more intimate, secretive, or delicate to be put in them.
Tartakovsky, p. 225
So in ‘may i feel said he’ the parentheses could represent the lovers’ embraces (protection and intimacy) with the shape of the punctuation suggesting the lovers’ arms encircling each other (iconicity).