There's no way of knowing how long it may take. Several weeks to six months doesn't seem to be unusual.
You're right about feeling your absence, consider also that at some point she may actually begin to lean more heavily on the OM to meet the needs you are no longer meeting for her. This may feel like she has stopped pursuing you and feel like a negative thing but it is usually the beginning of the end of the relationship with OM and a necessary phase.
She might eventually send you a message, one way or the other, that you two 'need to talk'. If at that point she tells you she has broken it off with OM and she wants to talk about your relationship, just be cool, listen to her with understanding and take it slow.
