Venus is jealous because psyche is more beautiful as a mortal and many of the followers venus had started to forget about her and they went on to worship psyche. it does make sense to be jealous for goddess of love because she represents the beauty and love, and if someone else takes her spot than there is no need for her.
it is fair for psyche for get help in her task because, Venus was doing all of this because of a lame reason, and psyche is not a god, so its hard for her to endure much, pain so a little help is needed.