Do you guys have any tips that's not on the wiki on how t get him back? (im on ps3)

Fast travel somewhere outside of a city.

Shadowmere is probably the buggiest thing since Oblivion. If he dies, it can get a bit confusing as to how to get him back. Some have seen him respawn back in the water in front of the Dark Brotherhood Sanctuary, others (including myself) have seen him respawn back in the same spot he died in. You'll have more luck with the second one. It's said he will respawn in the place of his death in 10 days, but I have waited for over 10 days and he never appeared. A couple in-game months later did he eventually appear, so I can't say the 10 day wait is quite accurate.

To be honest, there is no true easy way to get him back. I suggest wait 10 days and go back to the water outside the Dark Brotherhood Sanctuary and see if he is there. If not, go to his place of death.

yea I don't remember seeing him die, but on another playthrough I saw him fall through the world and he was gone. im not 100 sure where I actually lost him this time though heh

It's is almost impossible for him to die, he helped me to beat an ancient dragon, and HE was taking almost all the attacks.

yes that's why I want him back lol, though the spectral assassin is decent at tanking too

Skyrim Wiki:

• Shadowmere may disappear from the game entirely, however the spectral assassin still makes comments as if he were still present.
• Shadowmere may fall through the ground and disappear forever.

These two are possible, also if he randomly died, which is a bug too, he will respawn in 10 days in the same place he died.

Try waiting 11 days, and fast travel somewhere outside a city.

Tip: On XBOX waiting gets 70% faster if you press the Home button after pressing the A (confirm button), but I don't if that will work on PS3.