Trying very hard to not launch into a full literary critique of the song... it is apparently the expression of a person's inability to continue their expression of love in their relationship, and further, their resolution of accepting that. This is fairly concretely supported via the explicit statements such as "I can't keep lovin' you." Of course, this is later juxtaposed against the similar line, "I can't stop loving you," which illustrates the dichotomy of his two halves and their direct opposition to each other. In spite of this, the musical tone behind the words remains fairly constant through out the piece, suggesting that the speaker is in fact not at all ambivalent, but rather that he has already reached a conclusion. That conclusion is actually subtlely implied early in the song in the line, "Half of my heart's got a right mind to tell you that I can't keep lovin' you, oh, with half of my heart." To paraphrase, the speaker says that half of his proverbial heart cannot continue loving 'you'. While this is glossed over in the context of the song as simply restating the misgivings of this half of his heart that is 'a man who's never truly loved anything', it actually reaches into the other half as well. If half, or 50% of the speaker cannot love 'you', then there must be at least 50% that does not love 'you'. This also means that the amount that does love must be less than 50% and therefore the inability to love is not actually strictly limited to that one full non-loving side of his heart. This supports the consistent tone of the music, which together suggest that the speaker has already resolved to accept this 51+% percent of himself that does not love 'you' inspite of the 49-or-less% that does.