Shady bf

I have a nemesis at work and my boyfriend(who also works there) hates how she's always messing with me so he took it upon himself to message her and get her to say some pretty innapropriate things by flirting (she has a bf too) then went "ha! We've been f*ing with u". He told me all about it and showed me. But it as very upsetting that he did something like that w/o including me. I sorta feel cheated cuz they were some pretty nasty txts. And I feel it will only aggravate the already shitty work environment?  Am I right to be super ticked off?