Should I re-home my dog to a better family?

We have 3 dogs. A Chihuahua, a Pomeranian and a Shetland Sheepdog. Our Chihuahua and Pomeranian are the best of friends and play with each other all day. They never play with our Shetland Sheepdog and the Chihuahua often attacks him and doesn't let him get toys or eat sometimes. Also, we haven't had much time to exercise him at all because I am 8 months pregnant and very swollen and sore my husband works a lot. He is very bored and he seems extremely unhappy. He just stares at me all day and looks at me like "are we going to do ANYTHING?". He also has been picking up toys are running around growling with them in his mouth and barking excessively. I am pretty sure this is all because of the lack of attention that he is getting. I know shelties are dogs that need a lot of exercise and I feel really guilty about his quality of life right now. He is a really great dog and I know of a family though a sheltie rescue that really wants him and will give him everything that he needs. I think it my head that it is the best for him and for our family, because with a baby coming he will get even less attention. At the same time though I am very upset and have been crying hysterically for a week even thinking about not seeing him every day. I really don't know what to do and I don't know how to make the right decision. Does anyone have any advice for me?