Thanks to your advices guys, something interesting happened the same day I posted here. I talked to a friend about this issue, and she suggested that I take the risk to test his loyalty and to define the relationship by putting a label on it. Otherwise, I was constantly facing the problem of him taking too long to respond to my messages or calls. When I addressed this, he claimed he was busy most of the time. However, I argued that my work is busier than his, yet I still find time to keep in touch with him. Nevertheless, my friend added him on chat, and he accepted her. Then, they started conversing. To my surprise, he responded quickly to her messages while leaving mine unread for hours. Eventually, they both made plans to meet for a coffee date, but my friend ended up blocking him because it became clear to us that he wasn't serious about me.
I know it may seem childish, but at least now I have a clearer understanding of where I stand.