Yeah, tuna gets old after awhile. I mean, if the tuna is hot, you're eatin' it 24/7 for the first 6-8 months. That's when it is advisable to go looking for 'strange' tuna.
Then, you can go back to your old tuna, and it seems fresher. I suggest repeating that strategy as long as you can keep tuna #1 in the dark about all the different tuna on the side.
Now if tuna #1 won't take it up the ass, and you find a strange tuna that does, I recommend making that tuna #1, and throw your old tuna back into the sea.
Also, if you can get your tuna to dress up in french maid costumes and lots of leather and chains, that helps too.