I think this song is about his partner who is with him and says she loves him (This is the 'talk is cheap... give my a word you can keep'), but she wont really completely commit.
She's always wondering if there is something out there that's better and she's trying to decide if she wants to stay with him. He's telling her not to take too long figuring it out, because even though he loves her he's ready to leave her if she doesn't really want him enough. He's getting tired of it and even though he hasn't left her yet, he's already mentally and emotionally preparing himself for this eventuality. Thus, he is already halfway gone.
I think this song is about his partner who is with him and says she loves him (This is the 'talk is cheap... give my a word you can keep'), but she wont really completely commit.
She's always wondering if there is something out there that's better and she's trying to decide if she wants to stay with him. He's telling her not to take too long figuring it out, because even though he loves her he's ready to leave her if she doesn't really want him enough. He's getting tired of it and even though he hasn't left her yet, he's already mentally and emotionally preparing himself for this eventuality. Thus, he is already halfway gone.