Okay, not sure if I should butt in here or not but here is my advice.
First of all, as a Psychologist, I do not believe that the problem is truly the Yorkie. Most likely there are some underlying issues in your relationship that have not been dealt with and he is using the Yorkie as an excuse.
I also do not think that your bf has a control issue (I could be wrong, I am only going off what you have said here). His behavior sounds like a normal reaction to the amount of money you have spent for a dog that is a year or two away. From some of the other posts that you have made, it sounds like you may have an issue with compulsive spending. Ask yourself this: How do you feel when you make these purchases? Do you buy things that you really don't have any use for or want? Are you spending more than you can afford? How does it affect your personal relationships with others and your feelings toward yourself?
This does NOT mean that you are to blame for any problems in the relationship. It may just be one of a multitude of issues in the relationship that need to be resolved. It sounds like the two of you have not openly dealt with the issues of children, living arrangements, finances, and so forth that are key to any marriage being successful.
My advice is to go to pre-marital counseling immediately to work on these issues. I think that after the two of you work on these issues, learn how to openly communicate and learn some conflict resolution tools, you will find that he is much more open to the possibility of bringing a Yorkie into your lives. He needs to understand that every relationship is full of give and take and if you really feel a need to have a Yorkie in your life, that might just need to be one of his "gives".
Again, I might be completely wrong here, these are just my observations. If any of this is helpful to you at all, then just let me know where to send my bill
I truly wish you the best and think that with a little work (and any relationship worth having requires work) that the two of you will have a healthy long lasting relationship that others will be envious of.