OK, let's start with the basics.
YOU DO NOT EVER DIVORCE ONE MAN TO BE WITH ANOTHER.
For emphasis...
YOU DO NOT EVER DIVORCE ONE MAN TO BE WITH ANOTHER.
If you get divorced, you do it for yourself. Not for anyone else. Not because you love someone, you do it because the relationship you are in is personally damaging you more and more every day that you are in it.
Secondly, she's already cheating so this behavior of hers is going to continue and get easier for her to do over time. It's the nature of it.
Meeting someone online is not a real relationship. Meeting someone online is not a real relationship. Having a long distance relationship, is not a real relationship. You can start a relationship online, you can start a relationship long distance. You cannot continue any health relationship this way. She has delusions of grandeur in the new guy, and is making excuses to leave her husband.
I know this, because I've done it. I've cheated on my spouse. I've started a relationship online. I divorced my wife for my own sake, and apologized profusely to her for cheating... Even if the reasons for why I divorced her then, and now, were very valid. It's the worst thing I've ever done to someone.
The relationship that I was having when I divorced my wife ended badly. She blamed me for her personal issues caused by her own divorce and abuse by her ex husband. She blamed me for putting pressure on her. She blamed me for a lot of things and I stood there and took all of the shit she piled on me and blamed on me. She aborted our child. She repeatedly re-started the relationship with me only to **** me over again while she was sleeping with another person.
It drove me to the point in which I wanted to kill myself, went on anti-depressants, lost my job, blew through my retirement funds... It was really, really bad.
Your friend needs therapy. Really, she does. There's really no way she'd truly recover from the divorce, the shit she's done, and be able to be monogamous on her own.
If you have further questions I'm happy to answer them, but
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."