Jealousy Issue?

Me and my boyfriend have been dating for about a year now and everything has been great. I couldn't have asked for a better relationship or a better boyfriend. He is very loyal and is always wanting to spend time with me and help me out with almost anything I need help with. He's one of my very best friends and i've never felt more closer to anyone before, at least up until now. However, though I love my boyfriend quite a bit things haven't been so peachy lately....

It, of course, has alot to do with a few jealousy issues of mine and a close friend of his that is a girl. They've known each other for a few years and I honestly can say that I like her, she is really nice and is a good friend to my boyfriend but sometimes I can't help but feel a little worried from time to time. It use to never be this way until this summer had started. I use to always be so open and happy that she would hang around. I never understood where this jealousy came from until recently. It all began during a camping trip whenever I noticed my boyfriend's family getting along more with her and trying to always get her to tag along with us. It eventually started to get to me the more I thought about it and now I can't even hear her name anymore without feeling a heavy dread fill inside my body.

Lately, it's gotten worse. Even leading to fights. I trust my boyfriend. I know he would never cheat on me and I understand she's his friend he's known longer than me, but just how his family treats her it makes me feel like they prefer her alot more. Me and her have completely two different personalities. She's alot more outgoing than I am and more talkative. I'm more of the shy and quiet type who can hardly think of things to say. I've always been this way but i've been getting alot better at warming up to his parents recently, but somehow I still think they'd prefer her. They always try and invite her over and call her the daughter they never had since she acts just like them. It really bugs me and I can't fully understand why.

Even just this past weekend, after just getting back from a weekend camping trip, they decided to let her spend the night with them. They had let her watch over their dog while they were away and right as we were coming back to his house for the evening we had just caught her right as she was about to leave. She had told us she went ahead and spent the night last night without anyone there and they just smiled and said "Well, how about spend another night?" I about snapped. She was overjoyed. My boyfriend knew immediately how irritated I was and grew uncomfortable with the situation cause he knew how I felt about his friend but knew he couldn't do anything about it since it was his friend and he didn't want to be rude. They invited me to but I couldn't since I hadn't seen my parents all weekend and they wanted me home then and now so I couldn't stay. But that whole night I was stressed with worry and jealousy over the whole situation.

His parents know how I feel and find it a little hard to believe that i'm jealous. His mom even sat down and talked to me about the whole situation to try and straighten things out and it worked for a while but that whole feeling is gone now. They're very friendly and open people and I understand that, but that spending the night thing is what really got me and really hurt me. As childish as that may sound. They're even starting to get frustrated with me for getting jealous and find it very rude to compare who they like more, which I admit, is rude....

The friend of his even has a boyfriend of her own but they barely ever see each other and all she does is complain about him. She always just wants to spend time at my boyfriend's house with his family and even though I should be more open towards it....i'm more hesitant about it and not so happy anymore. I just feel like she should spend time with her own boyfriend and try and make the time to see him and his family more instead of my boyfriends. She's only met my boyfriend's family this year.

However despite all the jealousy, i've already told my boyfriend to never stop being friend's with this girl. No matter how jealous I get. Simply because I know how hard it is for him and that she really is a cool person once you know her. He tries to get us to be friends but where I get really shy most of the time it gets hard for me to and I get distant, but at the same time I really want to get rid of this jealousy. It's starting to ruin quite a bit already and i'm getting tired of worrying about this one girl. I just don't know what to do anymore and his parents aren't help by letting her spend the night every time she wants to. That really made me uncomfortable to the point I couldn't sleep.

So in general, is there any possible way to get rid of this jealousy and make situations easier for not only myself but for everyone else?