Montenegro has separated from Serbia and the Serbs don't really mind - as long as the Serb population isn't being ethnically cleansed there, and it isn't so things are actually going fine between Montenegro and Serbia now.
But even that was done with western puppet government manipulation - not allowing Montenegrins working in Serbia to vote while flying in ethnic Albanians from Michigan and New York (who'd been born in Montenegro decades ago) to vote and even allowing some in Albanian (near the border of Montenegro) and Kosovo to vote, lowering the requirement for separation to barely over 50%, etc.
Slovenes are free people. There’s nothing Srbs can do about it except annex with Belarus maybe.