Cutting meshes

I can't do art, and I can't do 3D art. But I can cut and paste and delete stuff...
But I ran into the same problem I ran into awhile ago when I was doing some clothing mods...cutting meshes! I wonder how I can deal with it.

Got a coat, but had to cut it up because (I think) I need to have the sleeves as one object and the rest of the coat as another so I can use the copynear bones properly, and this is the result



Look at that gap on her shoulder! It's horrible. How am I supposed to cut up meshes.