Eating asss

Well I feel really bad. Ever since i got pregnant I’ve been terrible at giving my man blow jobs and I have really been trying. I’m pretty much out of the whole morning sickness thing but it is still a struggle for me. Well instead he asked me to try to eat his ass. I was trying and trying but I just couldn’t. I’ve never been asked that and wasn’t sure how to and just I’ve never done it. I feel bad I want to please my man sexually but I feel like I can’t anymore. Help please