Hey their neighbor
I know that it is hard to grieve for Lexi and everyone grieves differently. My husband works in the city and gives me Yorkie reports almost daily so I know what you mean about seeing so many on the streets and how hard that must be for you.
All that I can tell you is from my own experience you will know when it is time. Lexi was a part of your life with your Bf that will always be there and it will be memories that one day will make you smile instead of cry. When it is time to bring a little boy home and into your lives you will know it in your heart. You can never replace Lexi but you can add a new chapter to your lives when you are both ready. Hang in there. You just never know what might come up that could bring an unexpected change to your life In the mean time, keep researching, learning and educating yourself and of course save your money so that you are well prepared when that time comes.