Dryer than the Sahara

Okay ladies! I've been with my boyfriend for five years and we've lived together for almost a year now. I find myself being super horny but never wanting to have sex with him! I love to masturbate and do it regularly but for some reason it just feels like work to do the deed with him. I love him and want to be with him so happiness in my relationship doesn't seem to be the issue!! How can I spice things up or figure out why I'm not interested? Has this happened to anyone?