Love Bird Breeding

I bought a peach face lovebird when it was still a few weeks old and has been keeping it for almost 3 years. As I notice it has grown in adulthood and I've been spending less time with it due to my busy schedule, I got it a mate, a female peachface (the first one is a male) This female is around 9 months old I was told. I am hoping to mate these birds, and has bought a nesting box and also addition food for them. They have been together for about 2 ~ 3 months, but I've yet to see them mating... I've noticed that the male is trying but the female does not seem to be too interested. The only gesture she allows the male is to get close and peck on her head and also something like kissing.....
Can anyone give me some tips as to how to get the birds to mate?