"With whom" is correct. Use "whom" after a preposition or for a direct object. Hence, it is correct to ask, "Who shot whom?" Of course, nobody says that and you would sound pretty dorky saying it.

I often tell T I missed her, even if it was only a week.

After a long absence, T has on one or two occasions replied, "I missed you too." I never doubted her sincerity.

I realise I can never be as important to her as she is to me, but I figure, a good mother has enough love for all her children and every one of them is special. Why shouldn't she miss us all?