OP: When you say you're not comfortable with anal sex, do you mean physically or psychologically? Or both?
Barring any serious medical conditions, anal sex is something that you can practice on your own (with fingers, then toys) before you get involved with someone. As well, a good partner will be patient if you haven't had much experience and be willing to take their time. Furthermore, when you're with a partner, hopefully you will have the opportunity to try being both a top & and bottom, so that you have an understanding of what is involved. Perhaps you'll discover that while you don't like bottoming, you really enjoy being a top (or vice versa...or possibly you'd discover you're versatile!)
If it's a psychological issue, you'd have to identify the specifics. Are you afraid it will hurt? (Again, practicing on you own can alieviate some of that stress) Are you afraid of contracting HIV or an STI? (Comprehensive safer sex knowledge for engaging in ANY sexual act is a must!)Are you plagued with the notion that it is dirty, or that it makes you less of a man to be on the receiving end? In cases like these, perhaps talking to friends who are sexually active in this way will help you to overcome some of the things that are troubling you.
This book may help you: http://www.amazon.ca/The-Ultimate-Guide-Anal-Sex/dp/157344121X
Regardless of this, you are not obligated to have anal sex with anyone. However, you also have to acknowledge that many men do enjoy it, and would expect it as part of their sex life when with the right partner. As such, you have to be prepared that he may say "Let's just be friends", which in the end will enable both of you to find someone you're sexually compatable with.