I'll play along with the astrology, just because I've read into it out of curiosity. I don't find it to be realistic, but here goes :)
Yes, we love to charm and be charmed. Yes, we love the ladies and the ladies love us. Yes, we are lovers of beauty and pleasure. Yes, we like amorous feelings and want to make others feel them.
But yes, we can be faithful. One thing about us Libra's is that we value romantic relationships seemingly more than any other sign. We just like to flirt, charm, love, and have sex plain and simple. It's a fun feeling and we get excited when those lovey-dovey feelings come around. When we experience physical beauty, non-emotional/mental fun, or sex but without deeper feelings, then it becomes a fun time for us. If we experience a deep connection but no romance and some level of interdependency, then she becomes our best friend and maybe something like a flirt buddy to make her feel good (because charming people makes us feel accomplished, after all).
What another star sign would say to their partner after sex: "Wow, that was great". To a Libra, it's flattering but there could be more. Change that to: "Wow, YOU are AMAZING!" Followed by a shower of kisses, then he won't be going anywhere anytime soon. You have to play into his ego a bit, and you also have to play into the romance game as well. Keep his eyes on you by firing back all of his romantic advances at you and let him know that he's loved by you, and he'll return the favor to you. Become a nagging wife, neglect any kind of intimacy (physical or otherwise), and basically let the flame die out--and his eyes will start wandering.
How's that for someone who not only doesn't believe in astrology, but isn't a "professional" at all? :D