How do you get used to the fact that someone you love dearly is slipping away from you?

What I mean is - you have pictures of this person; you know how s/he looks like; what his/her problems, beliefs, and wishes are, and what the general state of his/her mind is. You know how her/his face looks like.

Alas, you go out of contact. The person changes. Therewith, in time, the person you have in your mind ceases to exist - you just don't know how he or she looks like anymore (nor if he or she is alive). What to make of this as you go through your everyday life?