Family member heard me having sex !

I used to live with family members. We would only get busy when no one was home. One day my husband and I were having sex and I guess someone came home. Ever since that day , my husbands male cousin moans every time he sees me and will do it when my husband isn’t around. Mocking me I guess ? My question is what is the motive behind this? It bothers me, and I wish he would stop. We no longer live with them.