Okay, we have to remember that this is a comedy. It's pretty far-fetched. You are right; Oliver really has it in for his little brother. Not only does he treat him like two week old tuna, he hires a court wrestler to snap his spine. Eventually Orlando and the rest of the major characters end up in the Forest of Arden. Like most forests in Shakespearean comedies, it holds certain magical properties. Apparently it works as sort of calming of old enemies and aphrodisiac for young couples. Oliver goes into the forest to kill his little brother. When Orlando saves his life from a mean lion (lions in a forest?), Oliver repents and decides little Orlando isn't so bad after all. Oliver sees Celia and they fall in love in about three minutes; it must be that forest water! Yes, that is the transformation! We should have sent Osama Bin Laden in that forest with George W when we had the chance! Shakespeare's forests are the natural antidote to the harsh realities of courtly life. Characters can relax, let their hair down and listen to Beatles music; all their problems are transformed into love and friendship. Such is the case with Oliver and Orlando; the whole lion thing has little to do with it.