Light yourself on fire!

Hello. When you have a responsibility to a young, less self-sufficient animal that you purchased when he was just a little baby, isn't it IRRESPONSIBLE to purchase an even younger, less self-sufficient animal while your previous less self-sufficient animal is still in need of some MAJOR surgery to correct a hip dysfunction?
I feel it is inappropriate for one to justify the purchase of a second said animal by saying that it will be a playmate for the former animal. It is more than than inappropriate actually; it is cruel. Especially when the amount of physical exertion the former animal can do is hindered (except for swimming) by our veterinarian saying that he cannot even RUN with me. Now. Do you feel it is a great idea to get him a playmate just so he can RUN all freaking day in the backyard, just so I will have to rub his rips and give him painkillers at night?
He has playmates. He visits my father-in-law and plays with a Boxer typically once a week. He visits my mother-in-law and swims in her pool from sunup through nightfall typically once a week when he doesn't visit my father-in-law. He is loved, in excellent shape, and most importantly, he is happy. I love him, and I would do anything for him. If a $3,000+ surgery was not standing in the way of getting a dog, we'd be off to the clinic right now. But this is reality. We need to invest much money in Seamus as well as time for his rehabilitation. Is that fair to the new dog? Is it fair to Seamus, whose surgery we will undoubtedly have to delay due to incurring additional vet fees from our new investment?
This has nothing to do with "I take care of the dogs more." That may be so, but financially, we are both responsible, and I cannot look at myself in the mirror knowing that Seamus will not be getting his surgery due to incurring the additional expense of a dog who was supposed to be his playmate, but boy was our new investment surprised when they were trying to play with a cripple. That sounds like so much fun for everyone!