[yorkietalkjilly]

You didn't mention whether the male has been neutered and if he hasn't, he's probably miserable from the proximity of a female who may still have the scent of female hormones, etc., this soon after her spaying. The need to mate in un-neutered males is a deep compulsion with many of them and they are so miserable around any new dog, male or female, as they try to figure out whether or not they can mate with it. If he is not fixed, your task will be way harder (if not impossible in the short time you have) to stop this behavior as he is so driven by Mother Nature and not his own nature.

If he is fixed, it is probably his attempt to dominate and some dogs are pretty driven to control the other dog by that mounting behavior, especially if the other dog is acting nervous or in some other manner that the dominate dog deems unsuitable. Dominate dogs can try to control another dog's disliked behavior by intimidation first, such as mounting, and later by more aggressive methods.

But in any case, I would try to keep them separate unless you are willing to try and train him to leave her alone which may take a lot of your time and infinite patience from the sound of things. You might put him on a long leash so you can keep him off her if you can't keep them separate.