Divorce and going home

I'm in the middle of a separation (in the UK) with my soon to be ex. I want to file for divorce this year as I plan on moving back to the US by Christmas. I've had a look at the form and the choices gives to do with

1. Affair
2. Other party deserting you
3. Living apart for 2 years

I don't come under any of these. I am hoping I can have the divorce at least filed before I leave. Any suggestions? I rang the court and legal advice both can't give advice over the phone if anything. I work full time and can't get to the advice centrenwhen they are open. I'm trying to avoid having to take time of work as I only get paid what i work.

According to the DirectGov site:

Reasons for divorce
The court will only grant you a divorce if a judge agrees that your marriage is at an end. The legal term for this is 'irretrievably broken down'.

You must satisfy the court that one or more of the following is true as proof that your marriage is over:

•adultery by your husband or wife
•unreasonable behaviour by your husband or wife
•desertion for a period of at least two years
•two years' separation, if you both agree to the divorce
•five years' separation, if there is no agreement to the divorce

Another option to you is to file in the State that you'll be living in once you return to the US.

1. Affair

2. Other party deserting you
3. Living apart for 2 years

I don't come under any of these

what are the reasons for the divorce?

just to let you know,a divorce in the UK can take a minimum of 3 months. And thats if everything goes easy,no hassles and etc