My Neighbor's Husband

My my best friend, and neighbor's husband keeps making advances on me even in front of my husband and his own wife. I've made it very clear that I don't feel the same way toward him and told him to leave me alone. My husband knows about it, but he is a big wuss and won't stand up for me (the other guy is bigger than my husband). I've talked to his wife about it, and she's talked to him, and apparently they have had fights about it on several occasions. He won't let up. His wife kicked him out for 2 weeks because of it and told him the only way he could return is if he left me alone. He came back and didn't say or do anything inappropriate for about a month, but today I got a delivery of roses with a card in it from him.

It said, "I know the rules, but I can't help it. I love you so much. It kills me that you don't feel this way for me. Love, (name omitted)"

I shoved the roses through the mail slot in their door, and later got a phone call from his wife apologizing on his behalf.

I care for my friend and want to maintain a relationship with her and her kids, but I don't know how I can if he continues his advances. I feel involving the law would hurt my friendship with my neighbor.