he's saying that you can never be sure with relationships, but he'd rather be in one and seeing where it goes than waiting for the "perfect" girl to come around. he's not claiming to know for sure. you can think that you've "hit the lottery" and then suddenly everything turns to shit... or vice versa. but then he wraps it up by saying "although, i have a good feeling about this one" they both had a realization that you only live "in the now", to wait for something to just "come around" is foolish...that's why it's the first day of his life because he wasn't living before this time, he was just waiting (living in the future-which is not true living). both him and this girl had this realization although she had it earlier
in regards to the line about the lottery,
he's saying that you can never be sure with relationships, but he'd rather be in one and seeing where it goes than waiting for the "perfect" girl to come around. he's not claiming to know for sure. you can think that you've "hit the lottery" and then suddenly everything turns to shit... or vice versa. but then he wraps it up by saying "although, i have a good feeling about this one" they both had a realization that you only live "in the now", to wait for something to just "come around" is foolish...that's why it's the first day of his life because he wasn't living before this time, he was just waiting (living in the future-which is not true living). both him and this girl had this realization although she had it earlier