If it's the friendships you value, suggest to her that if you text/facebook a woman, it's only in the context of a GROUP message.

I feel that she'd fee way less threatened if you had the agreement of no individual connections.

I'm a single woman, and I can tell you, talking on facebook or text individually with the guy is a bad idea (usually). What starts as "Hey, had a fun time!" turns into "Hey, how was your day?" turns into compliments and light flirting on his end and unless all texts are being shared and approved by the girlfriend/wife, it becomes about me and him, not her and him.

It doesn't matter what you want, it's the proximity effect- more contact individually, more likely to catch feelings. Especially with someone you've already had sex with. Had this happen once, signals weren't clear, and feelings were developed despite having no desire for them to.