You tell her to stop texting her OM while in bed. She doesn't. She claims it's none of your business. Or that she's only texting her sister. You ask her to leave. She doesn't. You put grab her stuff and put it outside the door. She brings it back in. What then? You'd better think this through.
I did things without thinking it through, and it brought me to a place that I regretted.
Find a way to keep your dignity, a way to keep your integrity.
I feel for you, and I know you're going crazy. I wouldn't have lasted a night next to my W texting an OM.
ForG is right. Boundaries are something we personally enforce to protect ourselves and within our control. We cannot make someone else do something because we don't like it. That's not setting a boundary.
If he tries to kick her out, it will most likely play out like ForG said.
So, as I see it, you have one of two choices. Stay in the bed while she does what she wants, or you could leave the room, and when she asks why, you can tell her why.
The only way you can stay away from her texting OM while in bed is not being in the bed.