Sussing is the act of being shady in a relationship sense. Someone who withholds information about their other sexual partners and convinces someone they are exclusive. Playing with someones emotions.
Lexi: This man told me he loved me last week but he's been really sus lately
Sam: Did you ask him about it?
Lexi: Yeah he said there's nothing to worry about
~a day later
Lexi: This mans just texted me saying he has a gf!
Sam: Damn this guy was really sussing you!
Doing something sus. "sus a lot" or " sus little" can be used to describe how sus the action was.
Present simple: sus | Continuous: sussing | Perfect: had sussed | Perfect continuous: have been sussing