Possibly ot could be down to out of relationship activities , or the lack of them. When blokes are single they do bloke things, football , beer swilling, and other group like activities that keep them bonded. When a relationship starts these sorts of activities are slowly replaced unless you have a relationship agreement to some "own time" (note this is not the same as getting time out to hump your misses' sister/best mate/brother) this is time to do make bonding things like Saturday afternoon down the den, a Monday night pint or knitting circle (the latter may well be when you hump your other Halfs twin 🤐) I suspect that a lot of this feeling of loosing your mates is simply moving on from "lads activities" to "couples activities" where beer is replaced by wine, football replaced by baby minding and your mates are replaced by other blokes who have been tamed like you. I guess the solution is to accept the taming of the male , but have one day a week to rebond with your male friends, drink beer, eat curry and yell at 22 men plus a ref about how good, bad or blind they are. Maturity sucks my friend but get used to it lest you end up a sad lonely old codger with no better half 🤔