Another way to stop the clustering and maybe convince baby G to let your wife get out and get some Y time is for your wife to use her pumped milk straight after the first feed of that evening cluster....and maybe you should be the one to do this (as G will smell your wife etc etc),
Clustering in the evening is due to the lowering of prolactin levels as the afternoon and evening wear on....it is common as Shiv says, to around the 3-4 mth mark and after this, prolactin levels stay even throughout the day and night, only rising when LO is actually sucking. My DD particularly was a pain for wanting to be attached to me from week 6 to 10 ish at 6-9pm and I found it impossible to do DS's bedtime and this as DH works late. So I did a kind of top-up feed of ebm at this time rather than at DF time and it worked wonders for giving me back my evenings.
DS, on the other hand, was an easier guy for socialising as he clustered from 4 to 7ish pm in those early months.
It SHOULD all sort itself out soon and if not, I suppose take heart in the fact that the nights are so good....
S x