cecil wasnt selfish. look at it this way at that point in the game golbez could have just killed cecil and got the crystal if they had met. thing was golbez wanted to break cecils spirit more then kill him. cecil knew one way or another golbez would have ended up with the crystal wether it be by threatning rosa's life or by force. so cecil proably figured hey if i save rosa then not only do i not get killed by golbez and the world isnt destroyed cause im dead. but i have rosa on my side to help me fight golbez and im gonna need all the help i can get.

see cecil knew he needed rosa to defeat golbez he wasnt selfish he knew that golbez would end up with the crystal but why not have rosa alive.

also the whole cecil, kain, rosa triangle. i dont think cecil knew kain had feelings for rosa (as odvious as it was).