He's saying he's been out in the world, he's "felt the joy" and "learned about the pain", he's "met all the girls" and loved a few of them, he's smoked just a bit too much weed - - - in other words, he's experienced all the excesses of life, and everything he's been through has "opened up" his eyes. He's changed a lot, and the change is probably obvious to everyone. Now he's returning home after having "been away a country mile" (meaning, been a long way off) a different person.
He's saying he's been out in the world, he's "felt the joy" and "learned about the pain", he's "met all the girls" and loved a few of them, he's smoked just a bit too much weed - - - in other words, he's experienced all the excesses of life, and everything he's been through has "opened up" his eyes. He's changed a lot, and the change is probably obvious to everyone. Now he's returning home after having "been away a country mile" (meaning, been a long way off) a different person.