Glad my suggestions were helpful. I get that you are holding off on him saying I love you to Mia, but the reader needs to why. Just say it exactly as you wrote it below in his inner thought somewhere- perhaps at that moment I indicated in this chapter or in the previous one where I noted the same thing, or perhaps after he talks with his mom.
…he didn’t want to say it before she left because it might be too soon. And he doesn’t want the first time he says it to be on the phone. He wants to say it in person.