It depends on how much you love each other or how tolerate you are.
If you yourself is not faithful to your partner, you shouldn't take it for granted by expecting to be treated with the same "faith".
Whatever percentage of soberness is, I think this is just a totally rubbish excusses for a wrong-doing. But, under the effect of alcohol & fake-romantic environment, can someone assure that he/she can resist the "temptation"???. Ask this question: CAN YOU?

So, avoid from alcohol or going to those "fake-romantic" places (e.g. club or party). Even though one can say "well, I can control / protect myself", but, you can't keep yourself from those "hunters". You reject them once, the "hunters" will not give up and will try again and again until one day, when your mental strenght is "weak" (e.g. because of alcohol, loneliness, quarrel with partner, etc), one will get caught!!! Where... in bed, eventually.
I know a gal that she is very fond of clubbing / partying. I am not a clubber but I don't mind to go clubbing with her as if I want to take care of her. No other "bad" intention as I do love her so much. However, she refuses and says I will get boring as she sticks to her gal frd.
She told me she just clubbing and don't bother about other strangers. I kind of believe her as I got no choice as I can't go for clubbing with her.
Few times, I know that she didn't go home and she said she staying at her gal frd home, overnight. I trust her. She also used to get calls / sms from anonymous, who she met in the pub. But, she can't remember in the next day when she got drunk in yesterday night.
Until recently, indirectly, I found out something. She was once drunk and kissing with her ex-uni frd. I feel really disappointed and I start to imagine she used to be like that when get drunk during clubbing. I can't stop my imagination.

She even got into a trouble that a guy pretends as if her in the msn that "she" (pretended by that guy) likes one-night-stand. I helped her to find out that guy (a guy which is her frd and also a clubber). Finally, that guy stops doing that.
Though she just treats me like a normal frd, I questioned her and begged her stop from clubbing as I love her so much. But, she refuses and said she willing to face consequences on her behaviour.
I love her so much and I kind of "forgive" her again and again and try to forget what had happening. Somehow, it is too difficult to be so generosity.
What I hope now is she could realise and stop clubbing one day. Until my patient fading out, perhaps, I will give up on her.Hence, to all gals, please stop clubbing as it really bring no good to you and don't expect you could find a mr-right in clubbing / partying. No prejudice, but, I don't believe that a person would be "true" to you under the effect of alcohol and the "high" feeling when clubbing / partying.
Though it may be right to say that you just go to party for socializing. But, it would be better not get addicted to clubbing / partying and most important, not to alcohol.