The answer applies to every dog we've fostered. Adopting a 3rd dog would mean we wouldn't be able to foster anymore. When we first began to foster, about 2 years ago, my boyfriend and I decided that 3 dogs in the household would be the limit because any more than that and we didn't feel we would be able to devote the proper amount of care and time to each one. While there have been occassions in the past when we have had more than 3 dogs in the house, to do so on a continual basis, given our limitations, would not be fair to any of them.
We adopted Boomer, then Phoebe, our first 2 fosters. We could've easily adopted any one of the dogs that followed, but to do so would have meant an end to our ability to foster. And there were so many dogs out there, including Iris though of course we didn't know her at the time, that still needed our help. Adopting Iris, or any other dog, right now would mean we turn our backs on the other Irises of the world still waiting for their chance.
Aside from that though, to imply that Iris could not find happiness in another home, not only gives me way too much credit, but also does a huge injustice to Iris. Iris is full of heart. That she has come to trust me does not mean she is incapable of trusting another. She proved that to me last month when she stayed for 2 weeks with a very wonderful woman, her husband, and her family of 4-legged critters. In that short period, her fear at finding herself in a new place ebbed away and was replaced with the same comfort, happiness, and security I imagine she feels here with us. I am grateful for the opportunity that Iris had to bask in the love of somebody else other than myself. I want her to know as much love, from as many people, as possible.
It might be the easier thing to keep Iris permanently. Then I wouldn't have to take the responsibility of finding the right home for her, to trust that somebody else is taking good care of her, to worry and stress over how she might be doing, and I wouldn't have to experience the heartache that comes every time a foster is adopted. But fostering is about love, and love isn't always easy. There's always a shortage of foster homes, and there are too many dogs depending on us for me to take the easy way out. Iris has been through a long journey but it doesn't end with me. I'm just a guide that will hopefully help to lead her, as I have the dogs before her, to the happy ending she so richly deserves.