If the relationship has been decent, yes you owe him an explanation. You owe it to yourself to give one too.
This is one of those times when you aren't gonna be sure what to say, which is part of your problem. The tried, trusted and trite "It isn't you, it's me" and "Lets stay friends" will want to come spilling out of your mouth at some stage.
Don't let them.
If you like the guy well enough, but he is simply not the one for you, tell him the truth. Explaining it will hurt. Bowing out without explanation will hurt more.
I disagree with MM on this one. Just tell him point blank you aren't into him. Then leave. Explaning will accomplish nothing. Nothing you can say will make any difference - at all. It's not your problem how he handles it, and I suspect he will not take it well. I also suspect that's part of why you don't have any attraction to him.
I would say you owe yourself an explanation. An explanation why you went out with him in the first place. Otherwise, you will repeat the pattern. Time for some soul searching.
I agree with MM. Look, we ARE all humans---animals with emotions. In a troubling, confused world, we need to make sense of the little we can control. Yes, he needs an explanation. And it can be very simple, but it can be enough. Dont stress out too much. A "Hey___, I think we just need to end things because I fairly dont want a romantic relationship with you anymore" can help, because in the end, He might just be like WHOA, I need that to wake me up. To make sense of you and him.
Good luck. And RIP Steve Jobs.
Yes, give an explanation. If you were the one getting dump...You would want an explanation.
When I got dumped after a year and a half I wondered what the heck went wrong.
When I finally got an explanation (more than 6 months later) it was nothing like what I expected it to be and it wasn't very substantial, but at least it was something.
The difference in just a simple explanation (even if the best you can manage is still completely fulfilling) equated to weeks (or maybe even months) off the recovery time.
Explain yourself - it's the decent thing to do.