Is it normal that i feel animosity between my guys mom and me?

Okay. My boyfriend and I have been together for a little while and I love him. When I first met his mother/family we were just friends, and I would come over all the time to spend time with them. When I first met her we seemed to get along, so much so that I even called her mom and she seemed to like me. Well the problem began when we realized that we liked each other > apparently I am a little blind, because it too me way to long to notice this< , and i am almost positive that this is just me being dumb because it seemed like things for me and her went down hill from there. Even though she used to always tell us that we should just hurry up and get together. Now whenever I visit them i feel as if i am not wanted. He says that his mother has never really liked anyone and proclaims herself to be "Mama pain". I would like to think that maybe i just visit when she is in a bad mood but whenever I am on the phone with him before or after these visits she sounds perfectly happy. I want to just think that i am over thinking the whole situation. But my over thinking is Beginning to get to me. Whenever i hear her voice talking to him over the phone or even just seeing her walk around when we are on skype i get a little annoyed. I honestly love her > especially how he treats her< and i do not want to feel this way towards such a great women. So is it normal for my boyfriends mom to make me uncomfortable or possibly annoyed? Is it normal for girls to sometimes envy their guys mother? ( and are there any solutions to these feelings / I would love some responses from mothers to see it from their side)