Another thing ask yourself what did she get from these other men that she hasnt obviously got from you?If she got it from you she wouldnt look for it elsewhere.You said that you think they didnt have sex then its emotional support she needs and maybe there are things she hasnt told you about herself and she feels she cant let her know that you are not just interested in having sex and are interested and concerned about her feelings her as a person.I suggest you have a lot of self-gratification in private and start doing exercise to relieve your frustration and then make a sacrifice to be there for her for needs and listen to her and only her for a while when she feels loved again for her then she will feel better and then you will eventually get what you want as well.Maybe somewhere you lost the friendship and she looked for that friendship somewhere else.She needs a friend right now and you have to sacrifice to be there for her as one.Maybe when she offers sex say no and instead go for a meal or spend sometime cuddling and say what does she want and listen to her.Maybe she probably blanks out when you have sex because her emotional needs are not being met and feels unloved and just goes thru it for you like a great act.