Are inappropriate memes being sent to my gfs dms considered flirting if we're in a relationship and he also is?

Is it sketchy that my gf (29f) receives inappropriate memes sexual in nature from a client/friend that has a gf (30f) himself ? She doesn't tell me she gets them, I just notice his(35m) name pop up on her phone a lot at all hours so I got curious and checked. I scrolled all l the way back to last year and they were seemingly innocent at first but progressively started getting vulgar. I feel like he's sending out his tentacles to feel the vibe and see if she'll react certain ways which she hasn't. I find it real disrespectful that she kept that from me and she also hasn't told him to stop. The memes carry innuendo like wanting to get together or sexual situations. I've let it go on long enough, I'm about to just leave but I want to throw it in her face at the same time.