Hi I,

Perhaps she finally has enough trust in the relationship to be able to take your sex life to another level. Anal sex takes a lot of trust and sometimes it can help if the female takes charge as she can be in control of speed, thrust and penetration. If it was all on her terms it might have been more comfortable for her. 

Anal sex can be painful for some women, as the anus does not produce natural lubricants like the vagina does. Perhaps she applied some lube before she let you enter her. Maybe you were so wrapped up in the moment you didn’t notice.

Anal sex can be unpleasant for some and enjoyable for others, just like losing your virginity, some report a good experience where others suffer pain and bleeding.

It doesn’t necessarily mean that she’s cheating on you- unless there are other signs that make you suspicious. It might just mean that it has taken her some time to come around to the idea and she is finally ready to have anal sex with you on a more regular basis. Why not talk to her and ask her why the sudden change of heart? Discussing how it felt for her might help you to explore other positions and enjoy your new experience in the best possible ways.