I think it is hard that it is a holiday weekend. Did you have rituals you did during Easter when you were with your ex-husband? How long have you been remarried/seeing your new husband?

I am both a stepchild and stepmother and the "time alone" idea is very good. When my youngest stepson would come over I usually tried to stay in the background and just support whatever my husband and his son were doing. Maybe you can plan a weekend with your husband's children at their mothers so your son has you all's exclusive attention and your husband is in the background with you in the foreground? We had activities just the three of us did (camping) that were special. I would try to do things with just my son and also with just my son and husband so my son can experience the man for himself and without the other children.