I'm not sure I agree with the comment that he is selfish - for one thing we don't know whether it is intended that she would be queen or not, and it would be perfectly possible for them to be married and her not be a queen. If I'm right its been done before in this country, but not for a couple of hundred years, so it's not even breaking new ground.
Admittedly he bogged up his marriage big time and has no reason to be proud of his past behaviour, but his sons don't seem to have a problem with this. Yes there's the argument that while as a member of the royal family he should set an example, but there are a gazzilion threads here on Mumsnet showing far worse behaviour.
I sound like a right pro-Charles monarchist, but I'm not really. I just don't buy the "Diana was a saint" story. Yes she had very many good qualities, but the fact is that being human she also had a stack of bad ones too - the same applies to Charles.