Friend always invites herself wit me and my boyfriend

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Please read and give me your opinions/advice My best friend always seems to have to hang out with any of my boyfriends or guys that i've gone out with. She's also a complete flirt(sits on the guys laps, overly touchy, etc..) with them. She'll invite herself along with us and then act like that with the guy i'm with. Recently, I began dating someone who is actually one of her friends which makes this situation even worse. Whenever she's not with her own boyfriend she's with us. My boyfriend thinks that I like having her along since she is my best friend and therefore will sometimes even tell her our plans and she'll come along. My boyfriend and I were going to watch the races the other day and she called him and asked what was going on for the night and then she asked to come. She called me and told me my boyfriend would be picking her up and that she needed help moving something and made us over an hour late. This is really beginning to get to me but I feel like if I say anything I will be viewed as being jealous...Am I? When she called to say she was coming to the races with us and that he had to move something for her I hung up and drove myself to the races and met with some of my other friends to blow off some steam and my boyfriend and friend met me there and asked what I was upset about. By the next day my boyfriend and I were almost broke up because I "seem different" and "we aren't having as much fun". I told him I was sick of everything we do going through my friend and we decided to stay together.. However, last night my friend asked my boyfriend if she could ride to mall with us and he told her to ask me...That's not what I was looking for.... Am I being irrational with this??? Please give me some advice on what I should do... I'm sorry for the long post but I needed to get it out somehow. Thanks for reading and and advice would be appreciated.