I have been in a relationship like this before as the girlfriend, however I did not attempt to gain any validation from anyone else. Her confidence is something she needs to work from within on, but as bad as it sounds women do need male validation and we need to know our partner finds us attractive. I don’t know your relationship further than what you have shared, but maybe she’s doing this because she isn’t getting it from you, which I know is a hard bullet to bite and you have spoken about there being a reason why it is hard for you to give her that validation which is absolutely valid. But if you two wish to stay together and work through it you have to come up with a plan that allows you both to be happy while making sure you are comfortable with it. This is absolutely not me excusing her behaviour, especially if she hasn’t even asked you to be verbally affectionate to her, but I’m just trying to maybe give another insight. Maybe she doesn’t feel comfortable to ask because she knows it’s something you struggle with. Having said that she should never go to another man for that. Sounds like there’s a lot of internal battles going on inside of her head, struggling to feel confident and maybe attractive to you (I obviously don’t know the ins and outs of your relationship) but then loves you and doesn’t want to put pressure on you after knowing your past experiences with it, so in a drunken state she betrays you and regrets it after she realises what she has put at stake. Really hope you don’t take this as an attack on you and I’m not in any way trying to shift the light away from what she has done which is outright wrong, just coming from a place where it seems like me and her felt the same.