I don't think he will separate them, but rather, he'll serve to make them even closer! If he had been charming and good natured, I might have been concerned about a serious love triangle, but he's got a very flashy and over the top personality from what I've seen in the latest episode. So I don't think that Thapki will really form a serious connection. Especially since he's trying to marry her sister off, she'll probably have her guard up around him.
He'll probably fall for Thapki though, and he seems like he would be aggressive in his advances. Thapki seems as though she would be clueless, and that would probably awaken a protective and jealous side in Dhruv.