Analysis of an excerpt of Chopin"s piano sonata in Bb minor

[jlmap]

Can anyone help me to umderstand the sequence that happens at the end of the development of the first movement od this sonata? It is this passage: I can see that there is a descent in the bass from Bb to Ab, to G and to F, that suports 6th chords (g min, f min, e min and d min), and that there seems to be passage chords in between (Bb min between G min and F min, and an Aug chord between F min and E min, for example).But I cannot make sense of it.

[lelle]

M. 138-139: g minor
M. 140-141: b flat minor, which is a mediant to g minor, and iv of f minor
M. 142-143: f minor
M. 144-145: basically an augmented chord, created by the fact that he is using chromatic passing tones to go from f minor in the previous two bars to e minor in the next two bars: F-Ab-C -> E-Ab C -> E-G-B
M. 146-147: e minor
M. 148: G major: paralell to e minor

Notice that he never establishes a tonic, but keeps either the 3 or the 5 in the bass. This creates a sense of instability, he is searching and we don't know where he's going yet. We only get a chord in root position in M. 148, but it's not prepared with a normal cadence so we don't feel like he has established a tonic.

Here's a basic harmonic skeleton, might make it easier to follow along:

[jlmap]

Thank you! I was thinking a bit more, and maybe another way to look at this is: there is some kind of progression 64 -63. The first chord is Gmin 64. There is a 4th and a 6th. The 4th resolves to a 3rd, and we get Bb6. The d flat may be just a decoration, in orther to make a chromatic descent to the next group. Than, the D and the B descend an step, producing another 64 chord, now F min 64. The suspention 4-3 resolves when F descends to E, producing the Aug chord, that is also a 63 chord. This process continues until we get to a root position F chord, that is the dominant that prepairs the recapitulation. But, before the recapitulation comes a N6, followed by a new dominant. Do you think this is also a valid approach?