There are ways to help. Offhand, there are three common reasons people have for being unsure about giving their male partner anal stimulation. The first is "does this mean he's gay", and the answer is simple. No.

The second major issue is cleanliness/hygiene. This can be a bigger deal, but it's not that hard to solve. First, don't spring anal play on anyone as a "surprise", let them know ahead of time so they can go to the bathroom and make sure their bottoms are cooperating, and this will go a long way to minimizing yuckiness. Additionally you can put on a glove, which makes any mess easy to handle. If you're still concerned you can discuss the possibility of your partner taking a small enema/anal douche a hour or so before play to wash anything out of the rectum.

The third concern is one of hurting your partner. It's good to be careful - you can do damage if you are careless in anal play. Use safe toys, and if you're using fingers make sure that any sharp fingernails are either removed or guarded (wrap them in cotton balls and put on gloves). Use plenty of lube, go slow and have foreplay, and pay attention to what he's saying both verbally and nonverbally (but don't stop to over-analyze or do the "irritating waiter thing" and keep on asking if everything's OK - if it isn't it will be pretty obvious). less