"It's torment at times and other times it's fine. How do I make the switch? The easy solution is to stop caring. But I'm not okay with that."
No, you shouldn't be okay with that. Ceasing to care is seldom a good idea. You know, it's actually a pretty good sign that sometimes it's fine. It's normal to have spells of conflicted feelings, especially in the early stages of a poly relationship. You probably have a lifetime of monogamous conditioning to overcome. You have to be patient with yourself (and with the process).
What you may want to do is some digging into your internal processes to figure out exactly where these tormented thoughts/feelings are coming from. What is it that's causing you to feel this way? If it's her relationship with this other guy, what aspect of that relationship is the most troubling to you?
You'll probably have to ask yourself a lot of questions to get to the bottom of things. But, start with some easy/obvious questions, and go from there.