Standing behind the imaam if there are no other muqtadis
Q: I started performing salaah with the imaam and because another person was just there, I stood behind the imaam expecting the other person to join the salaah as well. But that person went to perform wudhu and we completed the whole salaah in this manner.
1. Is my salaah valid?
2. Should I have moved forward to go to the right of imam when I felt the other person will be late?
3. Is moving forward during salah permissible and how much can one walk forward before the salaah becomes invalid?