Been there. The bottom line is- two grown adults with secure relationship styles answer texts and phone calls within a reasonable period of time and freely talk about it as in “hey, could you respond to my messages, I know you are busy,etc, etc.” It should not be that hard, this is basic stuff! And saying my other GF was OK with it is nonsense. He is trying to put the blame on you and will continue to do so. You will always be clingy, needy, demanding, etc, when all you are asking for are things that are completely normal. Don’t fall for it!
In this day and age with smart phones, let’s face it..we all check our phones. And if you don’t, a normal adult would say I only check my phone in the afternoon, I work where there is no signal often(like the hospital I work in), I only check my e mail once a week, etc. I would not over analyze this, I have been there. He is just not that considerate.