Should I be worried about my boyfriend's new female friend?

My boyfriend started hanging out with a girl about 2 months ago. He says she is a friend from about 10 years ago but he never mentioned her before. For the first month I had no idea they were hanging out but I did notice his behavior had changed. It wasn't until I found movie ticket stubs (he has never taken me to the movies) that I found out about Jessica. He swore she was just a friend but he still would not introduce me. So, I followed him to her house! I went and knocked on the door and introduced myself. She acted like she wanted to befriend me and I almost believed her until she never once texted/called me but continued to text flirt/hangout with my boyfriend alone. I have never been invited to hang out with them. They go out for HOURS while I sit at home and both their phones will be off or otherwise unreachable the entire time. I've expressed my concern about this whole situation but he just tells me I'm tripping and that I'm psycho because they are "just friends" I have guy friends too but I am completely transparent and open about my relationship with them. I invite him to join us, I don't hide my texts, I don't disappear for hours and hours for alone time with any of them. He is acting like she is more important to him. He tells her intimate details of our relationship and bad mouths me to her! If he wants her vs me he should break up with me. But he won't! This is driving me crazy! I need your insight, advice please