My wife, who is the significant breadwinner in the relationship for 20 of the last 35 years I have been with her, has told me she has not had a strong desire for sex the past 10 years.  We have not had sex in over 5 years now and are both in our early 50's.  The last time I attempted to initiate sex with her two years ago (shortly after becoming unemployed) she refused saying she has no interest in sex.  I have not approached the subject since.  I am still unemployed but she hasn't divorced me and still talks of staying married into the future.  

My dilemma involves a work celebration party my wife attended for an individual co-worker on a Wednesday evening.  She attended this party instead of going to our daughter’s extracurricular event and neglected to tell our child that she would not be attending.  This was the second ‘celebration’ party for the co-worker a few days after the first party that my wife also attended.  However, this party was at the personal residence of my wife's former boss the past two years (former as of only a few weeks due to re-organizing), who happens to be the highest level employee of any party attendees (#2 in the company) and whom she had known and worked with the past 10+ years.  I only assume the party was likely 'without spouses' and don't know if the host's family was present.  I also assume the party was probably a dozen people or less and includes some co-workers who have worked together many years and are sort of their own little 'clique' that like to drink wine when they get together and are executives and high-level management at the company (#2 has his own personal wine cellar at home).  These are all folks making well over 6 figure salaries and the a few over 7 figure (host included).

After approx. four hours at the party my wife drove home drunk at 9pm with a nearly $200 bottle of wine as a ‘gift’ from her former boss.  She spoke to no one, went upstairs and showered for the first time in years before bed (instead of in the morning) and went to bed without speaking to my daughter about how her extracurricular event went.  When my slightly confused child asked why she was home and in bed so soon my wife replied she was ‘tired’ and fell asleep (or passed out, most likely). 

My wife is probably an alcoholic, as she has 1-2 drinks every night and occasionally more, although the nights drinking more have waned over the years.   However, she has just this year lost 25 lbs and is back to her normal weight. 

Does anyone have any thoughts as to whether/how I should ask her about the evening and what may have happened at the party (aside from the drunkedness)?  Am I overreacting to be suspicious of infidelity?  She has always denied it, but knowing her as I do since our high school years, there have been too many oddities and strange situations (i.e. - travelling on business trips with just one other male employee) such as this recent party over the years with her co-workers and alcohol (which is always involved to some extent) to make me think she has slept around with a co-worker or two over the years.