My mom is only happy when she's with her fiance?

I'm a 13 year old girl, and today, my mother and I ended up having a huge fight where both of us cried and yelled, etc. She said she was having a bad day. I asked her what's wrong, but she wouldn't tell me. After the fight, we were okay with each other, but my mom was still acting cold towards me. Now, she's been talking with her future husband on the phone for about two hours,and I've heard enthusiastic talking and laughing, and I feel as though my mom is only like that when she's with him. With us, she's distant, her mind is always somewhere else, and she never bothers to even really talk to us or ask us, her children, how our days are going or anything. She's only perky and happy with her fiance. Am I just imagining this, because I'm jealous of the fact that he can give her something that my brother and I cannot?