Letting emotions eat away at you isn't good for your health; both mentally and physically. Further stressors can lead to more and more overwhelming emotions (a bit of a butterfly effect) and thus a breakdown could be seen as inevitable. So, for example, if you get an overwhelming feeling of stress due to upcoming exams this may lead to a late period (sorry men!) and therefore may lead to a pregnancy scare (if you're sexually active) and more stress. It's important to face these emotions with full force; charge at them like a bull does to the colour red.
Words are the key thing here; they let you get things out in the open instead of keeping everything inside. So, when you feel an overwhelming emotion, write it down. Write about it. If you have upcoming exams for example, write about why you're feeling the stress that you're feeling. Write about those fears. Then lock them away, but if you feel these things again, write more. It may also be an idea to write about your options if things do go wrong, so for example, re-sitting. Have a look at what you wrote after your exams finish. If I was feeling stress over an exam I would write about how scared I am that I will fail thus my university dreams would be over and so on.
If you are feeling stress over a parent's divorce write about it. Write about what you're scared of. I'd been scared that I wouldn't get to see my dad any more.
The same applies to most situations. Overwhelming feelings over stopping self-harm, starting therapy, starting university, a pregnancy scare, an actual pregnancy, a partner that has cheated, if you have cheated, feeling anxious, going to the doctor and so on.
I hope I helped (^_^)