To control your thoughts, you need to discern what they are trying to express. Process the emotions they are trying to convey. Don't fight them and let yourself feel. Allow them to pass through. But in the process, evaluate, register and accept the concept in question. Accept the situation at face value and assess it objectively. Your thoughts stem from an internal disposition. Whether it's a breakup, substance or situation, explore the source and dissect it. Sometimes you have to remind yourself of how this concept has affected, helped, hurt or improved you. Thoughts are important and relevant. But remember to carry your logic too. Always uphold your integrity and self-worth when evaluating. Writing is a great way to physically manifest the idea of releasing these thoughts and provides relief. Write as much as you want, when you want and everything about this concept. The idea is to get it processed and discharged. Once you've done this you should have some clarity as to what direction to take, or perhaps with releasing it, you've let it go.