You could just re-write the forward pass in your model similar to this:
def forward(self, main_input, aux_input):
    main_input = self.embedding_1(main_input)
    main_input = self.lstm(main_input, (self.hidden, self.state))
    aux = self.aux_output(main_input)    

    aux_input = self.input_layer(aux_input)
    x = torch.cat((aux_input, main_input))
    x = F.relu(self.dense_1(x))
    x = F.relu(self.dense_2(x))
    x = F.relu(self.dense_3(x))
    x = self.main_output(x)

    return x, aux