You might be having repressed sexuality. Under the influence of alcohol, one feels disinhibited and act out on their inhibitions. But you are not comfortable with it, most of all your friends are male, they treat you as a guy and you love that most of the time, all these gives me a feeling that you may have gender identity problem. You should go to Psychiatrist and discus your issues. You may try online therapy also.
Keeping up the commitment is one of the most important problem in loosing weight. So you are not alone to face this problem. Set your target weight and work towards achieving that. Once achieved, work towards maintaining it. Never feel guilty about gaining again but be immediately active to loose that gain, right from single kg. gain.