I have been avoiding conversations with him completely, Starsky, thinking that's what I was SUPPOSED to be doing. I've been looking at ALL this as a "method." And I've left ME - and REAL LIFE - out of it. I haven't stood up for myself. I know that might not make sense. It doesn't even to me. I've just been a freaking robot, trying to tailor cool responses to him when he texts. I have not initiated ONE conversation even remotely related to our relationship because I thought that would be "pursuing." Verbalizing boundaries about ANY relationship with him, in my mind, has been a no-no because I haven't wanted to talk about our relationship.
Then think of it as healthy boundaries you need to have in place in order to negotiate the healthy END to your relationship, or -- if things should change -- at least to help you navigate this current period that he has indicated that he wants a relationship with OW instead of with you.
You're thinking of boundaries as tactics. THEY'RE NOT. They're not even strategy. They are healthy markers, for YOU, and for your KIDS.