Your sister in law may or may not be interested in you.How do you feel when she is around?It must be bothering you or you would not ask this question.I think I would throw some hints to your sister in law to let her know you are happy and would not be interested in another woman.Hopefully she will take the hint and leave it at that.This could cause problems if she is or isn't.Be real carefull how you handle this.Good luck