Try to figure out what emotional needs you have not been meeting and meet them. For example, she said "nothing happens anyway". That sounds like she notices the lack of touch. This does necessarily mean sex. It could just mean touch. Try offering her a massage, sit next to her so your bodies can touch, etc.
Whether there's another man or not, if she feels her needs are met by you, why would she leave? 180s are often meeting needs of the other spouse in ways you would like to do, but you ust haven't been doing.
Avoid the following: - statements encouraging separations of body or lives - saying things to pressure her to do something (give her some breathing room while staying nearby) - getting angry...as your sadness passes, anger or resent may creep in. Be ready and stay in control of your emotions - pretending you are happier now. If you are happier, then a D would only help more. Be honest with yourself and her in ways that show you have self-control. (ie, "I'm falling apart inside" instead of crying a storm) - treating her like a disease. If she asked for a D there was something wrong in the marriage. She should've been 'nicer', but she is trying to deal with a situation no one expects to be in. Try to look for those things wrong, decide on what changes you want to make for your life, and do them. - being impatient. She and you need some time to sort out tough emotions. Some words can't be taken back so easily. Patience will help you find a route out.
Good luck, DCB. Try to get some good sleep tonight so you can think clearly. If she allows you, hug her tonight and thank her for bringing up some serious relationship problems and tell her you're committed to re-examining yourself as a husband in the next month. Let her know that you'd like some time before making any decisions.