If I killed myself... if I die... it wouldn't matter right?

I had a dream...I woke up crying desperately...I was scary..I was scared of myself.. I was suicidal but that was years ago...but cause of that dream I was crying so hard like a mental person on bed...I promised my dear teacher that I won't suicide... but I think if I had a knife or a scissor near me at that time I would kill myself for sure.. I want to end it so bad..but the promise that I made kept me from chocking myself but what if it happens again and I won'tbe able to stop myself? I skipped school for 3 days cause of that but I have to go tomorrow... I thought I would be fine but now I'm thinking about it... I'm too nervous... I can't... for some reason my heart ache and my chest feels tight...I'm scared

Sorry for bothering... thank you for reading..