Help me! Anal?!?

Alright ladies, I have tried anal two times in my whole sex life. I did not like it one bit, it made a serious feeling of me having to shit and in one instance I shat on my ex. I was so embarrassed. My new boy and I have played with some things (vibrating bullet, his finger) and I still get the uncomfortable feeling of having to crap. He really wants to actually do it but he is waiting for my consent. Any tips?