We may be the opposite since I can't stand it when it takes forever for the leads to get together, but the first one I thought of was Shining Inheritance. It may not fit the bill exactly, and it's a bit longer than other dramas on your list (28 episodes), but it does take quite a while for the leads to get together (it's more of a slow build as it takes them a while to develop feelings as well). I really enjoyed the drama, despite the fact that the wait for them to get together drove me crazy, but you may like that about it, and there is a love triangle as well.