We've been together for about 6 months. Everything was great. Spending everyday with each other and just about every night. Then one day not too long ago it was like everything snapped. We got in some stupid argument over nothing and automatically she said she wants her space. She felt like I was controlling her and smothering her. I would always question her about everything she did when she wasn't with me. She started hanging out with some guy at work who is just a friend, and me being very insecure at the time, would get very mad and upset at this. Why does she need another guy in her life? Am I not satisfying her? Is she cheating? I would ask myself things like this constantly and let these questions manifest my entire thought process. Anyway... were on a break now and I hope to God that we can work things out. I HAVE TO LEARN TO TRUST HER at all times. Until she comes to me and tells me that she cheated on me then I must assume that she hasn't. I must not get mad at her when she tells me that she's going out with another guy. Yes this is hard but I must do it in order for our relationship to proceed and last. I must quit questioning everything and letting one negative thought lead to a more worse thought. It all comes down to fear. If I have no fear with her then her and I will have the greatest relationship ever. I must get rid of these negative fears and yes it will take practice. It's like playing the piano. If you practice at it hard enough you don't have to consciously think about it. It's just natural.
Am I going about this the right way in order to get rid of my insecurities/fears?

You're describing a not so nice habit in a relationship, and indeed "smothering" would indeed summarise this perfectly; it's all a matter of trusting each other, and not doubting the other's intentions. However realising that this isn't entirely right is the first step towards doing something about it, and willing to change it is the second step; now what's left to do is the next few steps, which means actually doing what you describe, and see how things go from there...

I do have to cut you a little slack though: your response is partially hormonal I think (male rival, rawr!), though that's not entirely an excuse and should not be used as such; and I think that if she sits down and thinks about this (and she has the time for that now, on a break.. ) she will realise this as well.

Give her some time, give her some space... but make sure the break doesn't last to long, or it might become a breach that is not so easily repaired.

Good luck!

Smoothing and non trust will kill a relationship but she should have put your legitimate concerns OVER her friendship with another guy.
How would she feel if you had a friend girl and told her YOU HAVE TO LEARN TO TRUST ME at all times until you tell her you cheated?

If you practice at it hard enough you don't have to consciously think about it. It's just natural. Your relationship/feelings should not have to be practiced at.

She wants a break in the meantime she can see this guy and leave you in "out of sight out of mind" mode. I think you should get your thoughts on IF you never get back.