Include the name of my interlocutor in my query (messaging system) - laravel

Question

I've a messaging system (1v1) on my website and I want to join some informations about my interlocutor (name, avatar, etc.).
My structure is more than common:
Threads:
Schema::create('threads', function (Blueprint $table) {
$table->increments('id');
//...
});
Participants:
Schema::create('participants', function (Blueprint $table) {
$table->increments('id');
$table->integer('thread_id')->unsigned();
$table->integer('user_id')->unsigned();
$table->foreign('thread_id')->references('id')->on('threads')->onDelete('cascade');
$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
});
To get my Threads I've this query:
Thread::select(
'users.name',
'threads.id',
//...
)->join('participants', 'participants.id', '=', 'threads.id')
->join('users', 'users.id', '=', 'participants.user_id')
->where('participants.user_id', '=', $user->id)
->get();
Of course, because of my where condition, it's my name and not the name of my interlocutor. How can I join the informations of my interlocutor and "exclude" mine?
PS: Please don't give me a messaging system package. I want to code it myself.
Edit:
Relation in my model Thread :
public function users()
{
return $this->belongsToMany('App\User', 'participants', 'thread_id', 'user_id');
}
public function participants()
{
return $this->hasMany('App\Participant', 'thread_id', 'id');
}
Edit 2:
#Jonas Staudenmeir code:
$threads = Thread::select(
'threads.id',
'threads.last_sender',
'threads.is_read',
'threads.last_message',
'threads.date'
)->whereHas('users', function($query) use($user) {
$query->where('users.id', $user->id);
})->with('users')->get();
foreach($threads as $thread) {
$interlocutor = $thread->users->where('users.id', '!=', $user->id)->first();
}
Trying to get the fields I only need:
$threads = Thread::select(
'threads.id',
'threads.last_sender',
'threads.is_read',
'threads.last_message',
'threads.date'
)->whereHas('users', function($query) use($user) {
$query->select('users.id') // May be its gonna run faster
->where('users.id', $user->id);
})->with('users')->get();
foreach($threads as $thread) {
$interlocutor = $thread->users->select(
'id',
'name',
...
)->where('users.id', '!=', $user->id)->first();
}
$intercolutor give me this error : Method Illuminate\Database\Eloquent\Collection::select does not exist.

Answer 1

Try this:
$threads = Thread::select('id', 'last_sender', 'is_read', 'last_message', 'date')
->whereHas('users', function($query) use($user) {
$query->where('users.id', $user->id);
})
->with('users:users.id,name,avatar')
->get();
foreach($threads as $thread) {
$interlocutor = $thread->users->where('id', '!=', $user->id)->first();
}