One of my closest friend is a man that I work with, purely platonic, I've never fancied him but we've known each other for about 6 years and have similar personalities / interests / similar ages and we often hang out and drink coffee or go for a beer. However, in the last few weeks a younger (about 10 years) colleague has started to give him lots of attention (including flirting with him although I don't think she fancies him), and I feel like I'm being pushed out of the friendship.
We originally spent time together as a 3 and she's quite a nice person, but recently she seems to be dominating his attention. When we are together I feel like I am excluded as she captivates his attention, and she occasionally makes bitchy comments about me (I'm not sure if they are intentionally bitchy or are meant in a playful, jokey way). Also, I don't really have anything in common with her and we wouldn't be friends if she wasn't friends with my friend. However, whenever I arrange something with my friend she has to be there (he makes sure she's invited), and recently they have started to arrange to do things together, which my friend always invites me to and I go along so that I don't miss out but then I usually feel like a spare part. I've tried backing off the friendship a bit and leaving them to get on with it but the only way I get to spend time with my friend these days is if she's there.
I feel increasingly jealous of her friendship with my friend ... I don't make friends easily so don't have a huge range of other people to spend time with. I don't want to say anything to my friend as he will probably think I'm just being paranoid, I don't really want to say can we meet up without extra friend sometime as then he'll want to know why, but I don't want to abandon my friendship with him either. Any suggestions about what to do?