I am on day 23 myself. Congratulations on making it 30, that is impressive. Also, well done for having the courage to admit your lapse. That takes guts.
I feel honesty and accountability are extremely important for us. I know I have never been honest or accountable for my drinking until now and it seems to have made everything easier this time round. Alcohol is all about secrets.
Come clean when he returns. My guess is he will respect you for your honest and his support will not waver. More importantly you will respect yourself and reaffirm that you want to stay sober.