Cracks and darkness between breasts

I’ve tried researching on my own about what this condition is or why I have it but seem to find nothing. For a few years now between my breast I have noticed that it is very dark and there are cracks indented into my skin (best way I can describe it)

I also develop little small bumps or pimples between them as well. Im just very disgusted, it is making me feel very insecure about my myself and I would like to know if any women out there have heard of anything like this, and is there anything I can do make this go away?