I'm not gonna tell this guy I'm talking to that I have a boyfriend.
Do you think this guy you're talking to is romantically interested in you?
Yeah, I think so, and I want to see if I feel the same way about him.
It sounds like you are stringing him along. That is very rude. You should be upfront.
I do what I want, and if I like the guy I will tell him about my boyfriend, and then we can go from there.
Intentionally not disclosing your relationship status to someone who is clearly interested in dating you is very selfish. He may not even want to date you if he finds out you hid this information from him for so long. It's also extremely rude to your current boyfriend since you are essentially trying to find a new partner while still dating him.