My boyfriend likes it when I finger his ass. I am fine with it but is it normal or strange?

Normal in a kinky kind of way.

There are tons of men that enjoy the added stimulation of rubbing and/or fingering of their butt.

The fact that you are fine with it is the coolest thing. You acting cool about it and not giving him a strange look or questioning his sexuality will make it very easy for him to be comfortable in his sexuality around you.

TIP: Although he did hint or ask you to play with his butt. I WAS NOT easy for him to bring
up. Dont wait on him to ask you to do it all the time, although he did ask you once, it
will make him alot more comfortable if he didnt have to ask. A man feels as if his "macho'" not gay ego is diminished by him asking you to play with his butt.