I completed Unlikely Valintine and invited Valintine to join me. Than I did Reunion and followed DogMeat. Once I got to Fort Hagen Valintine said something along the lines of "You should give DogMeat a rest, he's done enough".
I haven't seen DogMeat since. Where did he go? I looked around Sanctuary Hills and didn't see him.
Update: I didn't explicitly assign DogMeat to any of my settlements, he just left. But I'll check the Gas Station (as recommended in Where can I find Dogmeat after dismissing him to Sanctuary Hills?) and report back.