The first time I was brave enough to try it, just the thought of it seemed arousing. At first, the pain was like no other pain. Immediately I thought that if it continuied to hurt during the entire duration of anal penetration I would never again do it. After a few moments the pain became less. The actual pleasure began.
It's been over two years since the very first time I participated in anal sex. I don't remember the experience entirely. I do recall it was very pleasureable after the pain from being penetrated subsided. I remember enjoying it a lot after that. So much so that I wanted it again within hours.
If you are seeking advice to start exploring your significant other's anus with your penis remember you can never have too much lube. Lube will be her best friend during the experience. Go slow. As you begin to enter her ass it will be painful for her. Be sure to stop if she complains of any pain and wait until she is ready for you to continue entering her.
Unlike many others, who suggest using fingers and small toys first, I never did that. I just made sure his penis was well lubed as well as my ass. Worked fine. I had no patience for trying small things first for awhile before working up to the big bazooka. LOL! When I decided I wanted to experiment with anal I wanted to experience it fully right then and there not wait to graduate on to bigger and better things. Although that did happen much later. That's another story.
Anyways, enjoy exploring anal with your girlfriend, RobertJan.