Will bleaching my hair ruin the quality forever?

Hey.
My hair is medium brown and I would love to go to a blonde colour, mostly a white-ish blonde, but not too white. I have wanted to go to this colour for a few months now, but to be honest I'm really worried. I showed the hairdresser the picture of how I wanted my hair, and she said the only way she can get it like that is if she bleaches it. She also took a strand of my hair and highlighted it and it was just a light brown. So it looks like I'm going to have to bleach it. However, I was worrying what my hair conditions would be like, and if my hair would be all dry and frizzy. My dad also said since I have long hair, I'll be ruining it because im just going to bleach it all and it will be ruined forvever and I won't beable to get my brown back.
Can anybody please help me and give me advice on what to do. I would be EXTREMLY grateful.
Thanks!

Hi,

Bleached hair that is slightly damaged will feel dry or rough to the touch and may require extra applications of deep and leave-in conditioning products.

Severe damage to the cuticle, which is designed to protect the cortex where natural color resides, may result from over bleaching. The hair may be left spongy and porous with a tendency to retain moisture on following shampoo cycles and becoming difficult to dry out. The cuticle may be left feeling extremely rough or in some cases the delicate cuticle fishlike scales may be permanently damaged or burned off. In worst case scenarios hair breakage may occur from the root area.

However, this won't ruin your hair FOREVER. It will eventually grow out and be healthy again.

ok...
dont do it unless you go to a hairdresser I did a tiny strip in my fringe and now whenever it gets wet it goes like elastic and it breaks really easy.