Losing sexual attraction towards my bf

So I have kinda a weird situation, my bf of now 4 years, I love him with all my heart, I just have been noticing that I am no longer sexually attracted to him. We have been spicing it up I just haven't been enjoying sex with him at all. I feel guilty about it and he mentioned that he has been noticing. The other way around it's not he mentioned he hasn't had that at all... what do I do with this..