simple

hes obviously recently discovering new sexual urges which is perfectly normal.. most guys have them! you do need to talk and see if he is only attracted to men then he might be another closed minded gay! but if hes like most guys hes just got some hankerin for some cock.
Have a talk with him and decide whether it bothers you or not. And as someone said earlier you might get lucky and end up with 2 cocks to play with

 

Ok your boyfriend is either gay, in which case he pretends there is a cock on the other side of that ass when hes fuking u, or hes bisexual n still thinks hes shagging a shemale when hes havin sex with u.
My question is... does it not get messy? n if not, why?

 

How long have you been with this guy? I mean if you really like anal sex you can always find a guy who likes both. You don't have to be with a guy who is afraid to come out of the closet. He is sooo gay.

 

Speaking as an arse man, I love anal sex, however my current girlfriend has offered it to me but I prefer to stick with her very tight little pussy for the moment. Anal sex is something that is special I feel. I don't want to simply pop her butt cherry just because I want to. I want it to be a special time for us both.
If he is only interested in how he can get off, he is definitely thinking more about himself when he should be thinking about you. Especially when it comes to anal sex. That is something that, in my opinion, should only be done if it pleases both parties. If both people aren't being pleasured by what you are doing, then really it is simply a selfish act, rather than a loving act.

Hope that makes some kind of sense

 

Could be just a phase he's going through, or could be something serious. Only way to know is to talk to him.