The widely held belief is that if you're gay you're having anal sex, you love anal sex, and you will always have anal sex. The truth is that not every gay couple enjoys anal penetration so it's no guarantee that all gay men indulge in anal intercourse. That's a shame though; it's a pleasurable activity that can be enjoyed by both the giver and the receiver and it's possible that with a bit of knowledge you too can enjoy beautiful gay sex with your man.
The number one reason for the lack of gay sex via the anus is the pain that is often associated with it. If you don't take precautions there's almost always going to be pain, particularly the first time and nothing will ruin an arousing gay sex session faster than a burning in your rectum. Pain can be caused by hemorrhoids or anal fissures (and you should visit a doctor if you have either) but most likely it's caused by excess pressure and friction against the anus (or sphincter muscles, which keep the anus closed and prevent your waste from spilling out). To solve the problem of tightness you just need to relax.
Of course that's easier said than done. First, if you've never had gay sex anally then make sure you're comfortable with the guy you're looking to deflower you (or to deflower). Start with fingers and toys to loosen things up down there and make sure you use lots and lots of lube. You really can't be too liberal with the lubrication, including squirting some inside to make sure things up there are ready to receive. If you can have gay sex in the missionary position so you can look into each other's eyes and feel that connection and passion you might find it a great deal easier to relax and simply enjoy the pleasures that come with stimulation of the anus and of the penis entering it.
Pain is not the only reason men avoid anal gay sex. Hygiene and cleanliness are two other big reasons and they shouldn't be since it's easy to keep things clean down there. First, if you want to get really clean you can use a simple soap enema before penetration to ensure that nothing from inside you ends up on your man. You can also maintain a healthy diet with lots of fiber so your body largely does the job of cleaning things out in there. Also be sure to keep the area around the anus clean. Adult wipes (not baby wipes) are excellent for that but make sure they're free of perfume or any harmful chemicals that could make a sensitive spot burn.
Many guys abstain from anal sex because it's one of the easiest ways to pick up an STD. The anus is a thin membrane so it doesn't take much to get through it. Anal sex often comes with at least a little tearing and that opens things up. That's why safe sex is always preferred unless you're in a long term, monogamous relationship with someone you trust. Even then gay sex might be easier with a condom since it's a little cleaner.