You have relationship PROBLEMS because instead of being two equal adults in a relationship; you sound like a child begging for advice on how to convince her PARENT.... to get her a dog, instead of going with her BF in a joint manner, to adopt a "jointly owned" dog.
Surely, before you even GO to the shelter..... you have DECIDED whether the TWO of you can handle and do want the costs and responsibilities of a dog. You should not consider going to LOOK, until that is CERTAIN. After deciding you want to adopt, then you need to decide, as much as possible; what sort of dog (in size, age, coat-type, and activity level) - you are looking for.
WHY is there any EMERGENCY on this matter? WHY can you only get the dog TODAY? Why must your BF get the dog "FOR" you? - are you penniless? You sound pathetic, and UNDER his control. Make your own choices and develop a VOICE.
This should be a JOINT DECISION, not something you had to BEG for....... It will be even sadder (since you are so needy) if the dog bonds to him, instead of you (which can happen).