D.A.
My daughter had the same happen with her "boyfriend" in her first year of preschool. The two were inseparable that year. He moved to a different preschool the following year and she pined for him all that summer and still mentions him occasionally two years later. She wrote him letters, I emailed his mom for a playdate, we got no response from them and she was sad. She did make new friends the next year at preschool and that helped. We focused on playdates with new friends and some old friends and she isn't totally over him, but is doing much better. She now found a friend in Kinder that lives around the corner from us and is excited to have a classmate that has potential for frequent playdates. All of this is helping to get over her previous boyfriend. Oh, she has new male friends at K this year, too. She only mentions her old BF once in a great while, now.
Time heals and they make new friends. Try to make the contacts, and if nothing comes of it, she will be sad, but will get through it.