Ethics of war

Why did the Prophet have slave women?

Assalamu Alaikum - my question relates to sex with slavesWhy could the prophet (SAW) not restrain/overcome his rampant sexual desires when he wives?!?  This has really really shaken my faith.  I do not see how the prophet (SAW) is setting a good example here at all - as a Muslim I feel that family is the most important tie, with one wife a man should control himself and not have relations outside a marriage.  What possible justification is there for such depravity?  Please help explain this to me, as it is causing me some distress. Why shouldn't a man be satisfied with his wife or wives?  Why does he need to have sex outside marriage?  This is just greed and lust.  I've read a poor excuse that the poor woman in such a situation is fortunate because she might become pregnant and her child would be free and supported.  But why not just free her in the first place and support her?I hope inshallah you are able to answer my question, as this has been glossed over on many other websites with the strange claim that by having sex with her the man is somehow doing the women a favour.  This feels terribly unjust to me, and Allah has told us to stand against injustice.  Far better to free the slave and provide them with support, or just leave them be and support them - not seek some sordid gratification via them - treating them like property.Please please answer my question - I'm not received help on this from anywhere and I'm really worried about my faith