Lib dems are unionists first and their biggest promise is to remain in the EU. They wont be able to deliver that. Second best thing would be a second referendum. Labour has promised that so it makes sense that the Lib Dems work together with Labour to deliver a second referendum.
if the tories would promise to hold a second referendum to get the Lib Dems support it would be a different story since the tories and the lib dems have more common ground to stand on. So you might believe that the lib dems would do anything for some power, I dont see it that way, I believe its their duty to their voters to work with the party that offeres them to most influence to get their politics done. Brexit or remain is the biggest question in UK politics. Im pretty sure that the lib dems wont change their stance on that.