Can a man shave during the omer, if his wife goes to the mikva and wants him to shave ? Does shalom bayit trump all ?
There are times when shalom bayis may be factored into a halachoc decision, however it is not true that Shalom bayis trumps all. Oterwise it would be the persons spouse that decides the halachos for him and not chazal or Shulchan Aruch!
Regarding your question, unless you have some special considerations which you did not write about, it does not seem that it would be permitted to shave for this reason.