It's normal to check people out. I check out people in general. I don't do it to be rude, but naturally my eyes will wander. I won't gawk at a person. In your scenario, I think it may give a little more leeway since you are his ex so it's not like he's on a date with you, but given that he is still out with you, he shouldn't be gawking as that is rude to do with anyone. Your attention should be spent on the person you are with, not everyone else in the room.
It is normal to an extent. If the person who you are on the date is constantly looking/starring at another female, just get up and walk away, clearly that guy is not here for you, he is simply not there for the love either.
Well of course he would check you out lol, if he is checking other girls then I don't know what to say. We all look once in a while. If he is your ex then if he checks out other girls then maybe he is over it you know
We're human, we are made to be attracted to the opposite sex. However, I would be offended if it was a blatant "check out" and completely dis you while on the date. He should be tactful with his "check out." I know I've done it on dates, but I'm not rude or blunt about it.