S.C.
Baby may just miss you. If you are taking over at bed time then he is probably just tired and ready to sleep. It may help when you leave the baby to leave something that smells like you like a shirt you have worn. The familiar smell of mom may help him to calm down. Also make sure that your boyfriend knows that when the baby is crying the point is not to make the baby stop crying but to comfort him. Sometimes know matter what you try the baby will still fuss especially if they miss mom. Just like we would rather be comforted when we are upset even if it does not magically make us feel better it is better to just hold and love babies. They will not be spoiled if they are held a lot. No one goes to therapy because they felt loved to much as a child. Relax and enjoy the baby phase goes by so quickly and you will miss it when it is gone.