Go for questions like, “what’s your favourite food?” or “what movies do you like most?”. This helps you learn more about him and in doing so, you keep your conversation going while also showing him you care.
Say something like “We’ve been speaking for the past few weeks/months now and I have gotten to know more about you. Honestly, the thing is, I like you, I really do. And I know that you have a girlfriend but still I wanted you to know. "
If it’s just an “okay” or “thanks”, say: “I’m relieved now that I told you” . If he answers back in a long paragraph with the fact that he has a girlfriend and other excuses, just say “It’s okay, I wanted to be honest and I understand that you have a girlfriend. I’m okay with that”. If you get the answer you’ve been hoping for “I like you too”, just go ahead and carry on your conversation to see how things can unfold between you.