A libertine, according to the New Oxford American Dictionary, is a person whose behavior sets aside questions of morals and accountability, especially when it comes to their sexual and romantic relationships.
As the libertine is generally defined by their devil-may-care attitude, love, at least as how the Marquise de Merteuil defines it in the excerpt, would probably be inimical to the libertine. One could argue that establishing a stable, strong bond with another person goes against the freewheeling principles of libertines.
However, if one takes into account what Merteuil says right after the excerpt, it’s possible to see how love reinforces the libertine logic. According to Merteuil, it’s “enough for just one of the partners to feel” love. The other partner only has to “please,” which, when mixed with the “pleasure of deceiving” can be awfully exciting.
With Merteuil’s mischievous formula for love, the libertine can, hypothetically, be in a loving relationship without surrendering their wanton ways.
In Manon Lescaut, the conduct of the eponymous character can be compared to the behavior of Merteuil and Valmont. She could be seen as a libertine in that she deceives and manipulates Des Grieux. Yet it would be hard to say that Des Grieux is a libertine.
It’d also be difficult to claim that Saint-Preux or Julie act like libertines. They try to act responsibly, with Julie marrying and starting a family. Unfortunately, neither are rewarded for their relative adherence to virtue.