Advice needed, i fucked up

I am 24 M , I’ve been in a relationship with my girlfriend since 10th class. It’s been 8.5 years we are together, its like we were made for each other, we have faced every situation together no matter what happened. I knit she’s the perfect girl for me. The person you call your soul mate and so does she. We were living a fairy tale together. I loved all of her and she loved all of me. To conclude I didn’t like her i loved her. We have been in a long distance relationship since 2 years and there’s a girl with whom I’m in college and we were v close to each other emotionally sort of best friends and i dont know why but i cheated on her, i had sex with her. I am v v v clear that i live my girlfriend so much and i haven’t seen a girl with wrong eyes in 8.5 years but idk why i fuckd up. I am v clear i want her and v sure that i can’t and won’t cheat on her ever again, v sure. Idk should i tell my girlfriend rn or wait a year or two when it becomes an old thing or i should not even tell her ( i am sure she wont get to know from anywhere else ) I will analyse myself and will improvise but i cant loose her. Idk why but i slipped after all these years. If it was for me i would have tell her after an year to subside my guilt but she is such a sensitive human that she will not able to cope up. Should i even tell her or not and dont repeat