My boyfriend and sister....

Abigail
My boyfriend and sister work together. At first I thought it was fine, they'd be good around each other. But now, it just feels weird... They don't just talk at work, but they text and snapchat. And last night my boyfriend said 'I'm protective of you and your sister.' Just out of nowhere, straight up like that when we were laying down... Is it just me, or is it a little creepy? It makes me pretty uncomfortable, and I told him this, but he got mad at me. So I just don't know if I'm overreacting or if it really is weird!