I need some advice!

Me and my boyfriend have been together for 3 years and we have always been crazy about each other but in the past 6 months I have been going through phases where I don't have any interest in sex at all and then I do and I feel like it is starting to effect our relationship. He is all the time saying " I need your affection and you never love in me anymore." I tell him all the time that I do but I don't know what's wrong. Can someone please help me