If I remember correctly, the ratio of males to females should be 1:3 otherwise harassment may occur. With 3 females he has variety and can pick and choose. He MAY slap them around a bit but that's cool in the fish world, she'll like it.
What size is the tank? The sex ratio of one male to 2-3 females is accomplished best in a tank with plenty of space and hiding places. The only algae eaters I'd recommend to be lept with bettas is otocinclus catfish.