Looking at 1 Corinthians Chapter 7:
1: Now concerning the matters about which you wrote. It is well for a man not to touch a woman.
2: But because of the temptation to immorality, each man should have his own wife and each woman her own husband.
3: The husband should give to his wife her conjugal rights, and likewise the wife to her husband.
4: For the wife does not rule over her own body, but the husband does; likewise the husband does not rule over his own body, but the wife does.
5: Do not refuse one another except perhaps by agreement for a season, that you may devote yourselves to prayer; but then come together again, lest Satan tempt you through lack of self-control.
6: I say this by way of concession, not of command.
By looking at this as a whole: the last statement is something which I feel makes intentions clear of the above "I say this by way of concession, not of command"
So I personally take this is not a command, just different ways one can keep from sinning by lust. To me love or commitment isn't about lust, but love.
Also- I truely believe that Abraham, Issac, Jacob, David, Solomon, and many others were not sinning when involved in a plural marriage, and believe that God blessed them with their wives.