Not necessarily, but it could be damaging to your marriage, expose you to the prospect of paying child support until the child reaches 18 years of age, and it could be grounds for divorce.
Yes, it is.
No it is not illegal.
In most countries, yes.
you don't.
Yes, it is illegal to have a bill in someone else's name without their permission.
No. (Well, he could, but it would be illegal.)
It is illegal to alter someone else's check.
No it isn't illegal to purchase a car for someone else, but you will be responsible for payment.
Yes, it is illegal to tow someone else's car without their permission.
In countries where polygamy is illegal, this person will be in federal/legal trouble.
Physically yes. Whether it is permissible would depend on your cultural and religious belief.
yes because its not illegal