Coworker sending husband dirty memes

Sooo how should I feel about my husbands lady coworker sending him sexual memes? He sends her stuff back to. Idk how to feel? Idk if I'm reaching or if that's weird.

Edit.

Thanks everyone I really just needed reassurance because sometimes I over react. I talked to him when he got home and he said she dates someone he works with and shes 10 years older than him and it isnt like that. I put it in perspective for him by turning it around as if I was the one being shady and he got remorseful. He says he will stop replying to her. I'm definitely not done with the conversation but I'm feeling slightly better about it. I'm mostly worried about what their work conversations are like if they're sending things like that to each other. Going to continue the conversation when he gets back from the grocery.