I've always been bitter towards them because of our childhood breakup.
Is the breakup the only reason behind your bitterness towards them?
I was bitter before, during and after the breakup
You need to move on from a failed relationship. There will be another relationship in your future that is healthier for you but you need to move past the bitter feelings or you will be affected by them in your next relationship.
I honestly can't help myself.
Things like that can be difficult, I understand. But this happened a long time ago and you need to learn to move on. If you still find it difficult, a therapist could definitely help you out in the situation.