There's a few threads on anal sex and eliminating pain, but they got off-track. My advice on one thread was thus:
If it hurts, you're doing it wrong. I read that it's good for women to push out on penetration, and I am a great believer in using the right position. My penis is almost certainly much thicker than your boyfriend's, and I've enjoyed pain-free anal sex with women who were relaxed about anal sex and who used the right position. The two that worked best were a type of missionary position, woman on her back with right knee near her shoulder and me above, and woman on her stomach with legs spread.
Arousal is very important, the hornier you are and the more orgasms you've had the more ready you'll be. Surprisingly, the anal sex I've had we didn't use much lube, the first time just a little on her arsehole before penetration. But she was the expert after all.
This was my advice to someone like you, and from experience I know that anal sex can be pain-free with sufficient arousal, the right position and sufficient lube. I think it gets better with practice, because the girls I had anal sex with had a lot of prior experience and they did it quite easily.
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