Is it me? ....

My partner and I have been toether for 3 years. We've always had an amazing sex life! It's always been like it has from the start... until last night. I feel embarrassed even posting on here but have literally nobody to talk too. But I was giving him oral... and he went soft.. so i asked him what's up and he just said he didn't know, I asked if it was me he said no. But something's gotta be up? Surely? I feel so unnatractive now and I went downstairs after, was really upset and not once did he come to reassure me it wasnt me. Is it me? Is he bored? Is it normal? I'm enetering my fertile week and well, this has just put a downer on my mood now i guess. Any advice is greatly appreciated!! :(