Make mac mail VIP lists include items I send
Currently there does not seem to be a way to include sent email in the VIP mailbox. 

According to Apple's Mail User Guide – Show emails from VIP senders in Mail on Mac: "Any messages in the Inbox from  a VIP (even sent as part of a conversation) are displayed in a VIP mailbox." [emphasis added]

The conditions for Smart Mailboxes also only offer Sender is VIP and Sender is member of group.

However, you can create a new Smart Mailbox in the Mail app and add conditions of type Any recipient is equal to and manually add conditions with VIP email addresses to that Smart Mailbox. This way you could have a Smart Mailbox where mails you send to those recipients appear. 

See also Apple's Mail User Guide – Use Smart Mailboxes in Mail on Mac