Chins don't "love" each other. They are animals. They enjoy each other's companionship, but they may just as easily enjoy that same companionship with someone else.
You can't ask how long for this or that because no one can tell you. Chins who have lived together for 15 years may kill each other because the wind blew the wrong way. They may also take 10 seconds to bond, 2 weeks, or never.
After one of my chins has lost a mate, I immediately try and put them with another chin so they won't miss them. Almost always they take to the new mate with no difficulty and go on to produce more offspring, so no, they don't mate for life.