Why has Odysseus been away for so long?

He's been away because on the way back home from Troy (the Trojan war) he had to come home, but it was hard because he had to pass a lot of monsters, and shipmates mistakes and a bunch of obstacles and then finally a goddess Kalypso falls in love with him and takes him for herself on the island Ogyyseus or something like that and she wont let him leave. Then he finally gets to leave becauase Athena and every god but Poseidon because they believe he was a hero and deserve to go home so Kaypso releases him but then its a longer journey with more shipmates back to Ithaca again like he first tried to.