Torn mesh edges

Hi. While the weights are not transferred right and uv_1 could be better, re-doing these things will not help much. The item looks crumpled and torn because its topology is like that.
You must never use decimate on lod0, it just ruins everything.
If you have a version of this garment before you decimated it, go back to it. If not, join it into one again.
- clone a swimsuit for masc frame, export the blend, open;
- expand the rig, make feet selectable, select them, in 3d view press Shift D to duplicate, Esc to confirm;
- select feet.001, then the swimsuit, join both, rename to Reference;
- append your garment, separate hands from it. Rename the rest to Garment;
- select the garment, in edit mode select everything with A, remove doubles;
- transfer weights from the reference with the following settings, then use Clean with all groups and Limit total;
- transfer uv_1 again, this time it will be less torn;
- join the mesh back with the hands, give it cut 0000;
- clone ymBody_EF10Noctis, import the blend there

This mesh has A LOT of problems, and it will be every bit as much of a fight to clean up as the Resident Evil conversion tutorial I did. This was a scenario just like yours where the topology was horrendous making the mesh a nightmare to work with. It still didn't turn out all that well, in my opinion. Your UV islands are a choppy mess as well, and it's going to cause weird sharp edges in your mesh in areas you don't want them, and due to the wrecked topology, you won't be able to create nice sharp edges where you do want them.

Take a look at this screenshot. I removed doubles (M > by distance), then in the UV editor I pressed A to select everything then UVs > seams from islands. The red lines are the seams and they show where the edges of your UV islands are in your mesh.



My friend, this mesh in its current condition, will give you fits. I cannot stress this enough. Again, I have experience with this. I will ask you what Mauvemorn asked: Do you have a mesh that doesn't have such hideous topology and UV islands? If so, export this mesh as an OBJ, and start over with that OBJ. If you want to avoid what my screenshot shows, you will need to make straight seams in your mesh and afterward UV-unwrap your mesh so that you have clean UV islands. If you start with a mesh that has good topology this is easy to do. Literally, everything will be so much easier if your mesh has good topology.

That said, you have several rigs in your mesh — you need one rig and that's it — and several bone_bone_shapes. The bone_bone_shapes may be okay to leave in but why would you? It's easy to delete them. And you're going to have trouble with the sleeves because the armpits are so loose. Generally, you want the armpits to be close to the sim's armpits so that the sleeves will animate without crazy glitches. Look at EA meshes to see what I mean. Look at EA's topology while you're at it.