What noname said. Switch in new characters (lead with Melly, then Riki/Dunban, for example, works wonders), and build affinity. Then link dem skills!
You get skill trees from quests. I could list which ones, but one is in Colony 9, one in Colony 6, 2 in Frontier Village, one in Eryth Sea, one in Valak and one Fallen Arm.