I found out by accident last week that my husband of 23 years has been texting a woman from a company, that the company he works for has dealings with.

When I saw the messages I was so shocked, I couldn't breathe and felt physically sick.
The messages were calling each other darling, making arrangements to meet, asking if each other had woken up yet etc. The woman also sent him a highly sexual video clip.( not of herself)

When I confronted him about these messages he said it's just someone he needs to keep good contacts with to get a big project..., he said nothing sexual has happened, they just send messages and meet for dinner and that he is just mirroring her flirtatious messages.
He said he loves me and only wants me and is just using this woman to get a big project. He was really upset because I had seen the messages and I got so distressed.
I'm still in shock and feel really upset and uneasy about this bizarre situation,
I don't know if I can or should trust him anymore. He says the project will be finalized in July then it will all be over.
Has anyone got any advice?