Should i be upset about this? im not sure what to really think...?

probably about 4 months ago i started seeing this guy at the gym. we never talked but he would always make eye contact with me and say goodnight to me as he left. nothing really happened but then about a month and a half ago he came up to me and said that since he usually sees me there that maybe someday we could run together. then he gave me his number and told me to text him or call him....well since then we've texted each other everday almost all day. weve called each other countless times. when we talk we can talk for hours. we just get along really well and we're becoming good friends. i figured we were just getting to know each other before we really went out anywhere together...and then he just told me that he has a girlfriend. he said that we still can talk, that it doesnt change anything. Is it wrong to be a little ticked that he hasnt told me until now? I know i shouldve probably thought it was weird when we never hung out outside of the gym, but i was ok with just getting to know who he really was first. anyway, i was starting to like him and he springs this on me. if something ever happened and we dated should i be wary that if he would go behind his girlfriends back to talk to me, that he would do the same type of thing if we were dating?...and now that i know he has a girlfriend ive backed off to complete friend mode now too