I am having Thanksgiving woes?

Okay, so i have been dating my first for 4 and a half years now. So last night while we were playing monopoly and spades he kept staring at my older sister. And not just staring but looking at her the same way he looks at me. I was right there, why wouldn't he look at me? Everything he did or said for the rest of the night was directed towards her. I felt like the third wheel to their party and he is suppose to be MY man. It has made me lose a lot of interest in our relationship. I want someone who only has eyes for me or can at least keep them to himself around my many sisters. I do not mind him glancing at strangers but the way he acted towards her is really hurting me. He hasnt acted differently with me or anything, he is still very loving. What should I do?