It may be time to get a free consultation. You may need to get a separation agreement in place which lays out child support, visitation schedules, and requires court approval for either parent to take the children out of state.
You also need to be clear about what you want if she brings it up again. Tell her you want every other weekend and maybe one or two nights during the week. I would think she would be happy to have the help with their homework and such lol. How far away does she want you to stay? Would Boise be far enough? You can always compromise for the short-term, sign a 6 month lease somewhere, and reevaluate in 6 months.
Out of curiosity, what's in SLC that she would go there??? (You don't have to answer this, but in all your vague religious references, you've never mentioned a particular religion. Are you guys Mormon?)