Dead on interpretation of Dom's words, in my opinion.

I've been working on the Letty-personality I keep getting and one reason I can't see them having survived forever (barring needing to not be alone, which kept them together so long) is that Letty, to me, feels as pushy-alpha in her own way as Dom. As long as she's Dom's girl, she's not first...they love each other to death and back again, but her need to be best at something is possibly why they don't always click. (Evidenced by Letty having been out of his bed long enough for him to sleep with Tran's sister).

I love Dom/Letty...but I treat it like Robin/Batgirl...they eventually grow out of it.