He, previously to falling in love, couldn't understand why people gave up so much for love. So much, they gave up who they were before hand, and put their entirety into the relationship\love. Now he has found love himself;
"I can't believe I finally found
the key, the door, the trip
it was all in my mind
now I'm one with the fools of love"
I could be wrong, but this is my interpretation;
He, previously to falling in love, couldn't understand why people gave up so much for love. So much, they gave up who they were before hand, and put their entirety into the relationship\love. Now he has found love himself; "I can't believe I finally found the key, the door, the trip it was all in my mind now I'm one with the fools of love"