Q:

Is it possible to relate a table on a pivot one with eloquent ORM? 

These are my tables many-to-many:
products and suppliers, however I need to relate the pivot(product_supplier) to a table called payment_supplier. 

Product model
 public function suppliers(){
    return $this->belongsToMany('App\Supplier');
}

Supplier model
 public function products(){
    return $this->belongsToMany('App\Product');
}

but I need to relate pivot product_supplier to payment_supplier table just like described on the diagram

A:

In this case, you could use a pivot model. 
# Product Model
public function suppliers() {
    return $this->belongsToMany(Supplier::class)->using(ProductSupplier::class);
}

# Supplier Model
public function products(){
    return $this->belongsToMany(Product::class)->using(ProductSupplier::class);
}

# ProductSupplier Pivot Model
<? php
namespace App;

use Illuminate\Database\Eloquent\Relations\Pivot;

class ProductSupplier extends Pivot
{
    public function payment_supplier()
    {
        return $this->hasMany(PaymentSupplier::class);
    }
}

However, doing it like this has a big problem: You CANNOT eager load a pivot's relationships.  Not without an override (or a package). 
The other way to go about it is using hasManyThrough
# Product Model
public function suppliers()
{
    return $this->belongsToMany(Supplier::class)->using(ProductSupplier::class);
}

public function payment_suppliers()
{
    return $this->hasManyThrough(PaymentSupplier::class, ProductSupplier::class);
}

# Supplier Model
public function products()
{
    return $this->belongsToMany(Product::class)->using(ProductSupplier::class);
}

public function payment_suppliers()
{
    return $this->hasManyThrough(PaymentSupplier::class, ProductSupplier::class);
}

This gives you every PaymentSupplier for a single Supplier/Product, so you'll need to apply some kind of filtering.