Why would he do that?has anyone of you guys done that before?

I was getting to know this guy for 1 month now,we texted everyday, talked about our kids, well finally i decided to ask him out, which i did, but he told me that he has a gf, i was shocked for sometime and couldn’t utter a word out of my mouth,not to mention that i felt very rejected; however i took a decision to end the friendship and told him well if you have a girlfriend we shouldn’t be talking, because obviously i like you and it would not be fair with your girlfriend. He replied me "no she has been very supportive of our friendship”; however i still insisted on stop talking, because i have feelings for him and i believe it will make it a very weird friendship for me and his girlfriend, again he replied " like i said she is very supportive of our friendship i don’t see why cant we talk”. Now what i think is that,either he does not have a girlfriend because he is a doctor always at work, divorced and have 2 kids and his beautiful kids live with him. Or he is just not ready to see someone as of now but at the same time does not want to lose me, which i totally understand, its some part of some people’s nature. What do you guys think?