What exactly is a Trojan?

Is it possible for my partner t spy on me from his house to mine via computer... or was my friend spying on me and telling him everything i am doing??

What exactly is a Trojan?windows

let me first explain what a VIRUS is.

a VIRUS is software which only ever tries to get onto more and more computers, and copies itself from one computer to another.

a TROJAN however is software that when installed on your computer will 99% of the time allow a certain person to access your computer through a backdoor without your knowledge. the level of this access varies, from simply logging everything your type to being able to watch your screen in real-time just as if they were watching over your shoulder.

the answer to your questions is dependant on a few factors, does your partner have physical access to your computer when you're not in the room? or do you just run any files you're sent without scanning them for viruses and trojans first? if neither of the above apply, it's probably your friend rather than being a computer issue.

EDIT: why is this even a computer question, from your additional details you're just saying your boyfriend wants to have a threesome with your friend, and that he's admitted he's spying on you etc etc - whether you reformat your computer or not it will make no difference to the problems in your life even if he never messes with your computer again.