I don't think Clark is shocked by Mayson's interest in him. He'd have to have been pretty dumb not to have figured out that Mayson really liked him when she kissed him in Church of Metropolis.
I do think, however, that Clark is torn. He's in love with Lois, but she persists in treating him only as a friend. I think he likes Mayson, but he really likes the attention that she gives him. Everyone wanted to feel loved and appreciated, even Clark.
As for telling Mayson that he cares for both her and Lois , I think this is the result of the fact that he hates conflict and hates hurting people. He does like Mayson, just not in the way that she wants him to. It is a cop-out, but I don't think he's leading her on intentionally.
