Quite often it happens that A loves B, B loves C so A backs off, maybe he tells B that he loves her but B tells him that she is sorry but she loves C… then somehow the relationship between B and C end!
B does not goes back to A thinking that A may not love her any more. Well, that might have happened with time but often if love is deep then it stays quite alive, and if they had no bitterness in their hearts A may still wait for B.
So if B decides to return to A she should be really honest with him, no shoulder to cry on thing, that would be nasty. Inhuman most probably! A on the other hand should clearly tell B that even though their relationship did not clicked in past he is still waiting for her, and will absolutely love to have her in life.
Love is too precious a gem to be lost over miscommunication or lack of communication.