I'm in love...but with my sister's hubby

I have been living with my step-sister in Kitale and she is married to a good husband. Her husband actually educated me through high school and college and even got me to a job. Recently he told me he loves me and wants to marry me as his second wife.

I like him very much because he has been there for me but I am not sure that this is the right thing to do. I know this is bad but I love this man and I too want to be happy. Does the law allow this?
{Lillian}