I think a lot of unfair assumptions are made of married men or men in real life relationships and have second life relationships.
Noperson engages in an online relationship unless there is something missing from the real life marriage or there is a desire that is not being met. Marriages and relationships can become stale and sometimes embarking on an online relationship can actually save the real life one by allowing that person the freedom to explore areas of sexual behavior or practices that their real life partner would constitute as perverse or at the very least something they don't enjoy.
I would suggest that there are many men and women who without the release of cyber or virtual sex would have real life affairs - They see online relationships and sex as a "Safer Option" Lets be honest it IS the safer option. Its a lot easier to tuck yourself away in a room with the desktop or laptop than make excuses to go to the "Gym" or go on a " Work training course" on a regular basis and see your lover in RL. Lets be honest if most people discovered their RL partner was having virtual sex they would be far more forgiving than if they found a pair of panties in the glove box of the car.
I know of several couples that are in very solid happy marriages/relationships. They both engage in online relationships and sex and they enjoy this mutual escapism, sharing stories of their intimate encounters and SL and other virtual sex mediums are just another form of erotica they use to enhance their sex lives.
The moralists can say its cheating if you have online sex because you are engaging in a level of intimacy that is above the level of friendship. In fact I came across a case in theUK where a divorce was granted on the grounds of "Unreasonable behavior" That behavior was the husband having an online sexual relationship. While the judge could not declare that an adulterous act under the marriage act he found that the amount of time he spent online with his online partners to the detriment of his real life marriage, caused distress and upset to his wife and lead to the breakdown of communication and a decline in marital relations.
After six years in second life I find that there are just as many women as men engaging in online sex and relationships. Yes many are hidden from their real life partners often because of some of the reasons I have mentioned. They want to explore everything from **bleep** to BDSM to Role playing - They don't want to break up the family home in RL or embark on a RL affair so this is the safe alternative. For anyone to say that they should be upfront and honest about what they do in SL with their wives/husbands/partners I would say that there are a million reasons why a second life is hidden.
I have spoken to quite a few married guys about the reasons they have online sex and there are a few reasons that are very common.
1. They have been married many years and their partner is no longer interested in sex. They have a good lifestyle outside bed and to break up would be emotionally and financially destructive not only for them both but for children too.
2. The RL partner has over many years made them feel that they are no longer attractive, The bald head and pot belly has come along with middle age and its been so long since they had a compliment or made to feel good. Second life allows them to reinvent themselves and to feel attractive, wanted and successful with women once more - This also applies to women who embark on SL relationships.
3. They have always wanted to be dominant, sub serviant, have **bleep** sex, role play everything from doctor and nurses to slave and master - Sadly RL partner isn't one to oblige so rather than seek that satisfaction in RL and break up the family unit then second life provides that outlet.
4. I simply enjoy the eroticism of mutual masturbation with a stranger who may live several thousand miles away. My wife/partner knows I **bleep** all SL does is give me a fun way of enhancing it.
The real problem in SL as regards married men (or Women) engaging in online sex and relationships is when area;l life emotions start to come into it. When real life photos are exchanged along with personal information including phone numbers. When online sex becomes voice sex, when Second life becomes entrenched into real life - That's the big problem. The virtual life diminishes and start to take over real life and fatally damage the real life marriage and family.- The UK divorce I mentioned being just one of thousands of examples.
Ultimately we have no right to judge anyone morally as no one has the right to insist that everyone lives by the same moral and ethical code. It is down to ourselves to decide what we define as acceptable behavior choosing our friends, relationships and living a life that conforms to it.