In my opinion, he's not going to take your concerns or your boundaries seriously when you're flirting with him in text messages, WHILE he's with OW and has made no commitments to you. I know it feels good to get a reaction out of him, but it's NOT going to help your cause.
In fact, it's very possible that he and OW may be sitting there getting a laugh out of them at your expense. I know that sounds really cruel, but I've heard dozens of similar stories and you can ask WDID or Sandi or any of the other FWAWs.