It may not be that Mr. Bennet's "crossed in love" reference is cruel (especially since he did not say it in Jane's hearing in the text). Instead it may have been (what he considers) practical truth based on his own experience of being crossed in love in his own marriage. He may have been reflecting how one must make the best of the setbacks life hands one. That he tries to give it a witty turn is not surprising in Mr. B's case.

That is not to say Mr. B did the best job of handling his marital setback; but I do not expect him to see that very clearly. Still, he is offering some sliver of good advice on Jane's case if Bingley is truly irretrievable.