Why does my husband ignore me when we're around his family or friends?

My husband is my best friend, we talk about everything and is always social and affectionate EXCEPT when we are around his family and friends. He becomes a completely different person, he will ignore me and leave me to fend for myself for hours at parties. He won't make eye contact or even come over to see how I am. He is normal around my family and friends. We've been together for almost 10 years. FYI: his family and friends are very cliquish and not overly friendly. WHY, WTF, I don't understand.