Do i have a right to be jealous about the girl who works with my boyfriend?

My boyfriend works in a big property firm but most of the people there are 40 plus he and a few other guys are quite young 24. Recently a new girl started whose my age 20 as the receptionist. I didn't think anything of it at first, but my boyfriend has recently started to talk about her constantly, he tells me she is pretty and really really nice. He says she's really like me and we could be twins etc which to be honest i don't take as a compliment. He goes out to the pub with her and clubbing with her a lot although he said he'd never go clubbing with me as it would ruin the balance of a boys night out yet he would take her?. He has stopped taking me to work events since she's on the scene. He cancels things with me so he can go to the pub with her, he was supposed to be seeing me tonight which he bailed on so he could go to the pub for this girls 21st birthday drinks. He brought her a bottle of champagne and flowers and a card for her birthday yet hes never brought me flowers in our whole 2 years together. She texts him a fair amount and they now end up having lunch together everyday. I don't know if im over reacting but i feel really upset by it, i clearly cant tell him off as she works there but i think there spending a lot of time together and whenever i bring it up he defends her and paints me out to be the insecure clingy girlfriend. I feel like im goong slightly mad as i don't know if theres something to be bothered about or im over reacting

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