You need to be relaxed and excited so you can loosen the anal rings and penetration could be more enjoyable.
Since you have had two painful experiences I'm pretty sure that the only thought you have on your mind whenever the other guy is making his advances with you for anal sex is a pain in the ass :eek:, am I right?. You know I am. What you need is a little training:muscle-flexing-smil. Here´s what you can do:
Go to a sexshop and search for three things:
1) A butt plug, not so big of course, so you can get your anus used to the sensation of having something inside it.
2) A dildo that resembles a Porn Star penis, I mean, that its material is very similar to the skin texture. This way you'll be able to practice with something more accurate to reality regarding to the sensations. Plus being a porn star penis, it would have a good size and with time and practice you'll be used and prepared to handle almost every boner you find. :tongue:
3) A bottle of water based lube, so you can lubricate both butt plug and dildo.
Practice in private and take your time. One of the benefits of doing it alone is that you decide when and how it's done...you don't have the pressure to please anyone, if you start feeling any pain you can rest when you need it (while in a real sex intercourse you might feel obliged to wait until the other finishes).
A great tip that helps you when you're practicing with a dildo is to be excited; excitment opens the anal sphincters and gets your prostate to feel pleasure whenever it's rubbed with something. A porn movie, a sexy magazine, a creative brain will make the trick.
Always use the lub, and if you can put a condom in the dildo (get used to be protected while practicing).
You don't have anything to loose giving it a shot, and a lot of pleasure to get. You'll feel more confident, your body will be more prepared and won't suffer anymore. The only secundary effect could be that you get so hooked on that you'll never want to see another guy:biggrin:...Just kidding!!!. :tongue:
Just do it!. Cheers and wish you the best of luck