wildwood,
You probably don't know *exactly* what a given gay couple do in the bedroom. Not all gay men have anal sex - trust me.
Regardless, if it's anal sex specifically that bothers you, then just remind yourself that heterosexual couples do it too - other couples that you know have very likely engaged in it.
If you're still bothered by it, then I'd invite you to ask yourself why people even ought to be 'normal' in the bedroom. Why is 'normal' sexual activity better than 'abnormal' sexual activity? (Providing it's all consensual, of course). There's not really any way you can prove that doing what's 'normal' is better. Sex should be fun - and if people don't enjoy 'normal' sex, it doesn't make sense for them to indulge in it.