Assuming that you live in the U.S, regardless of how long he's been separated (even if it's been decades) he is still married until he goes through the legal process to obtain a divorce.
No, to be legally divorced you have to apply to a court and go through all the required legal steps. Separation does not of itself alter the fact that you are married to your partner.
No
Some states require proof of divorce to hand out marriage license while some don't, however if you are legally divorced I do not see any problem. However by honesty it's always good to let your actual partner know that you are a divorced woman/man, otherwise it will start causing conflicts between you and your spouse.
A legal principle called "estoppel" bars people from using subterfuge to escape contractual obligation: had he signed "mickey mouse", it would still be considered a legally valid, binding document!
no, not from you, but from him yes
If said first partner is dead, then it is legal.
Yes. You can have a live in partner, but you have to be completely divorced in all states to get married again. You should be aware that living with another person while your divorce is pending may have an adverse impact on the outcome of your divorce. Make sure you speak with your divorce attorney before moving in together.
Divorced or partner dead but still with children.
It depends on which country you're getting a divorce in. If the country is Australia then you must be legally separated from your partner for a minimum of 12 months before you can be eligible for divorce. Otherwise, please change the question to specify a country.
NO,u should try to convince your partner that families are not burdun but a healthy sign of backup.
The only two ways you can legally change your name and use it officially is with a marital status change (actually getting married or divorced), or to legally change your name, which is a lot of paperwork. You could get charged for fraud by using a false last name for health insurance purposes. You could also get into trouble for adding yourself to a partner's insurance if there are no domestic partner laws in place in your state. You MUST check into domestic partner laws before doing anything so you don't get hit with a really nasty lawsuit from the insurance company. If there are domestic partner laws you can take advantage of, there is absolutely no need to use a false name in the first place.
Possibly; many states have laws about disclosure of STDs to your partner.