Why did he get nasty when I wouldn't keep in touch, he was going back with ex wife.

Can you give a little more information please.

Because he was hoping on having you both.

Because he wanted to have his cake and eat it, or to have you as his bit on the side, or his reserve.

To advise you more we need more information. Your question is far too vague to warrant anything other than speculation.

Because you shouldn't be just a "piece on the side" and he knows it.