I think my husband likes my sister

Okay so this is really weird but it's something I've been noticing. Lately my husband has been talking about my sister all the time. He's always asking me to tell her to come over to hang out or asking when she's coming over or asking where she is. He wants me to invite her to every single thing we do. He added her on snapchat. And he's always weird around her when we do hang out. It's just a little strange and uncomfortable for me. I'm pregnant and I've gained a little weight. We never have sex anymore and he doesn't show a lot of affection towards me. I think he's just not attracted to me anymore. I don't know. But I can tell something is up with him and I think he has a crush on her.