Not attracted to my boyfriend anymore

We have been together for 2 years x he is always there for me and we have a flat together , he is such a nice guy I love him to pieces the thought of him being with someone else kills me x he is really close to my sisters and cares about them deeply and they care about him x we have went through losing a baby together and he has helped me through depression x So a cant leave him but kissing him and sex is more like a chor for me x when we got together I was so attracted to him but now nothing x when I talk to other guys it flatters me and I feel excited but I feel guilty for my bf xx could this just be faze