very interesting point guys, well this is my guess
to hook up
to have a steady relationship
to be committed
As previously mentioned by some of you the specific term "ficar" might be a slang, as a matter of fact, a brazilian slang.
However, considering the variety of verbs we have in English we are still tied up to the context. Summing up,
to flirt= flertar
You shall try saying "I'm flirting with Maria" if you guys don't have a steady relationship like "namoro"
once you guys have already decided you both wanna be together and it means no other people involved, you may try saying
"we have a steady relationship"
now let's imagine you are at a party and someone keeps looking at you and you notice that she/he might be interested in hooking up with you (ter algo com você, quem sabe uns beijinhos). You can tell this person "Im sorry I'm committed" (sou comprometido)
a different background..
Your mother suspects you are seeing someone because your always neat and clean and the only thing you do is keep on calling this guy/girl.
she might want to ask you "are you seeing anyone?" "Você está encontrando com alguém?" Aha! Some of you might think no, it means "ficando com alguém" but the thing is, What's the definition of "ficar"? Do you necessarily have to kiss someone in order to do that?
and what about to date?
I've seen many people in the states using the verb to date when they were having a steady relatioship but also an unsteady relatioship.
So as you could see, we still have to be aware about the context ok?
JMO-> in order to get the closest as possible of the meaning "ficar" try on using "to flirt" all right?