Bruce listened to everything Clark had to say, before he realized exactly what it was about this that was bothering him. That realization struck like a lightening bolt and suddenly he really understood.

He understood why he was uneasy with the idea, he understood why he didn't want to talk about this with Clark and did tend to wall it off and hide it, and he understood why it frustrated Clark and what Clark was trying to get around.

"I love you." The sky was blue, the grass was green, and nothing was new. "I'm completely willing to do some - maybe even a good deal - of this to you, and I will enjoy it. The thing I'm trying to keep you away from isn't masochism. It's using someone else to abuse and punish me. That's not a role I want you to fill, and frankly I don't think it's a role you want to be cast in, either."

There were two totally separate issues there. Hurt him in sex, yes, god, please. Take him apart? Was... a different kind of masochism. It was pure expression of loathing, albeit self loathing, not love. The thing Clark was offering was out of love and he'd take that.

But he couldn't ask, and wouldn't let, Clark do the other.

Fine line, but intent and psychology and Bruce more than action, but still important.