Most Helpful Guy
I would make it very clear to your guy friend that you are not interested in a relationship, and that flirting with you is not appropriate or appreciated.
Tactfully draw a line in the sand if you feel like he's trying to be more than just friends.
As for him texting you all the time, ignore those texts, don't engage in conversation. Eventually he will get the hint.
If he doesn't let up, tell your boyfriend and let him deal with it if he wants.
Most Helpful Girl
Of course this male friend of yours texting you and flirting with you, especially considering how he's already told you that he likes you, is bad. Which I'm sure you already know.
You should remind him that you're already in a relationship and would appreciate if he backed off.