There are numerous reasons why a marriage fails.
In my case, a 29 year old marriage ended, and the reason given was crossdressing and transgender issues. Although, I have to stress that except for visiting sites like this, I did not dress or even own any female apparel for the last 5 years of the marriage, in order to keep the peace.
However, there were financial issues as well. Except for very brief temporary work, she hadn't been employed for over 6 years. After paying for various schooling that she desired, she had 2 degrees and spent her time looking for, and applying to, jobs that she felt were worthy of her. Her job became 'looking for a job', and refused to consider any employment she considered to be "beneath" her. While I worked a full time job 6 days a week, and part time work when I could get it.
Being exhausted and stressed out from trying to keep us afloat and bringing in the money to pay the bills left little time or energy on my part to get 'cuddly' with her, which she resented.
But, she found a way to satisfy her physical needs... with the neighbor.
The trans & CD stuff was just a convenient way to avoid accepting any responsibility for the failure of the marriage.