I believe:
You are DIVISION and I am DENOMINATOR
My prefix is my abbreviation.
My infix is.
My suffix is seeing something.
Together, I need someone like you.
Prefix: DIV is the abbrevation for DIVISION, common in programming and proofs, and also the prefix
Infix: IS is the infix for DIVISION
Suffix: VISION is seeing something
Together: You need a DENOMINATOR to perform DIVISION
My prefix is a place.
My infix is eating something.
My suffix is suspicious by its presence.
Together, you cannot let the one like me be nothing.
Prefix: DEN, a room or wild animal's lair is a place
Infix: NOM, to eat something loudly or with enjoyment
Suffix: TOR is an open source tool for anonymous communication and web browsing, that while having legitimate uses to protect privacy, has gained notoriety as a tool used to carry out illicit activities online. Suspicious!
Together: DENOMINATOR cannot be 0, otherwise DIVISION is undefined