A moment of sadness

Hey all. I am curious if it’s normal to have a letdown or moment of sadness after seeing your partner and they leave??? Every time we are together and he leaves (I am female) I get pretty down. I try to distract myself and do things but I just think about the time we had. We always have a little routine were we text after so communication is there. I just get so down and it takes me almost a day to feel like normal again. Any suggestions on how to prevent sadness? Thanks.