Yes it's ridiculous and unfair. The dog won't know if it's coming or going and realistically there is a good chance it will end up being given up.
Sit him and his gf (and ideally friend) down and calmy worked through the budget - does he know how much insurance is and food, how much yearly vets annual bills and monthly flea/worming prevention is. Does he know how much one off dog bills can be, and the usual excess with insurance.
Is it a puppy or older dog - either way it probably won't be able to be left alone for a while. Have you asked them how they are going to be at home with it all the time, what they plan to do with it if they go out in the evening before it can get used to being alone. Do they know how much a dog boarder costs if they go away over night and have you made it clear you won't be stepping in.
Ask them about the breed, do they know the challenges with the particular breed. Ask what they plan to do if the dog has aggression issues etc, or isn't toilet trained, or who will pay/Fix things if it damages them (ie chewed furniture/scratched doors).
Have you explained how many dogs go to rescue and how unfair it would be unless they can all completely commit and understand how this is going to work for the next 10 years.
His gf and friend are enabling this so you ideally want to talk with them all. You only need to persuade one that this is a bad idea.