The minute you allow someone to disrespect your relationship and your SO is the minute you show the world how little you think of both. If you value your SO, and your relationship is important to you, then if (or when) someone seeks to slight either one - you have an obligation to speak up. Even if it makes you uncomfortable, even if you normally prefer to simply get along with everyone.

Allow no one to belittle what you have. Be loyal and loving to your SO and the relationship you have worked so hard to build.