If you rush Catalyst then don't play tear. To me, Seraph's Embrace is not a good item on Singed. It only have 250 AP and about 120 at lvl 18. And you have to charge it full. I know that toggle now work with it but buying make you more lack of sustain. If you didn't stay in the fight long enough at late game. Then you are a burden to your team.
Its mana shield is not something you can count on. They could wait until it on cooldown and take you. Hope you will make it better