It’s easy to urge tripped up in these quite situations—I know I did. You’re involved someone, but things don’t seem to be moving along as you’d like. But you’re afraid to mention something because you don’t want to look needy/weak/desperate/etc. Many folks are conditioned to think that posing for clarification on a relationship status puts us at a terrible disadvantage.
I would suggest asking this question from an edge of power instead of weakness. the general tone shouldn't be “Do you wish me?” or “Will you ever want to be serious with me?” But instead, “I got to know where this is often going, if anywhere. i actually such as you and need to remain friends regardless of what, but i want to understand if there's potential for a relationship here, because if not i want to maneuver on.”
Or something thereto effect. the thought isn't that you’re trying to find his approval. You’re trying to plan your life, and you’re allowed to some clearness from him on what your relationship status is.
As you say though, there's the possibly of rejection. From the sound of your letter, it seems like you've got already taken the important step of accepting that you simply might not hear what you would like to hear—and you furthermore may recognize that that's preferable to being strung along.
So that’s great—you’ve already taken a key step to starting this conversation from an edge of strength. Once you accept that the conversation might not go the way you would like , you'll also get clear on the very fact that, however painful this might be, ultimately you’ll be fine.