Welcome to theLoveLogic forums,
First and foremost, do you want to get to know this guy better? It sounds very odd to me as well. Since he has already metioned a girlfriend why do you still seem a bit interested? THe fact he said it means, "I am not going to get involved with you on a romantic or dating level". I think you are doing a GREAT job being aloof and just being you. Sounds like he is the one with the maturity problem.
The way to not be played is NOT to play. Keep doing what your doing and don't worry about this one. If he genuinely liked you, he would pursue you.
Don't let his text messages and "good enough" friendship get the best of you.
Take care of you!
Thanks for joining us Elizabeth!