What´ s going on...
Your cousin does not seem have children, though you have not mentioned and you appear not to be married yet.
But what intrigues me now is, why is your BIL not taking such a young wife to his work place for so many years?
Is that marriage going ok? Is that only due to visa or some such problem of convenience etc? The second question is, were you in love with her before her marriage itself, did she marry her husband against her wish instead of marrying you?
Think, answer, identify the RIGHT problem and then try to solve.