Gem man and his quick change

A Gemini man has been with the same girl for years, he calls her his best friend, better half, soul mate and considered marrying her and starting a family with her. Said girl stuck with him through thick and thin. They've been building a life together. Something Gem appreciates because he needs stability and understands he can be airy sometimes and hates it. This girl is her ground.

He logs on Facebook one day and sees an ex posted on a friends wall. An ex he dated for a week only. It was mostly sexual, and it was a string of bad sex meetups. They broke up because the girl was into partying and didn't wanna be in a relationship.

He talks to her, and in 2 days they reconnect quickly. The girl is now in a relationship but having issues, she's a mom, but only stays to not break her family. They talk about meeting for coffee and they do. Later that night, Gem and the ex talks about dating when the girl is in a better situation.
The same night, Gem talks to the girl he's currently with and explains that he wants to see how things can go with this girl. That when he met her for coffee and hugged her, it just felt right. That it's something he needs to explore.

The current girl is devastated. Doesn't know what to think. Tries to explain that it's not how relationship works, but Gem man apologize, tell her he really likes the way he feels for the other girl. They talk. Gem say he doesn't wanna lose her because she's his everything, yet wanna try with the other girl and tells her he's confused and don't know what to do or think.

What should the current girl do? Give him his space and let him go explore risking the whole relationship and do what he wants OR be his rock and keep him on track?
I remember someone here saying Gem can be like kids, that they need to be sit and explained what they're doing wrong.

What do you think should happen here?

On one side.... It's not a nice thing to do that after he's committed and has started making a life with her.

On the other.... At least he told her first before he cheated on her.... Cudos for at least that cuz most would/do just cheat.

There's nothing she can do. Looks like he's made up his mind. He might change it again, but I wouldn't hold my breath on that one! She just needs to let go. If, and when, he cones back... It's up to her whether she takes him back or not. I wouldn't!

*comes

Classic. He wants to put his relationship with you on pause while he makes sure the other girl isn't a better deal. He'll probably be back, but I would feel justifiably insulted if I were in your shoes. The best thing to do is not to bitch, moan, fight, or fall to pieces, but to simply let him know that you are a human, not a CD player, and will not remain in suspended animation in "pause" mode until he decides if you are the best choice. Perhaps you need to do some terribly exciting things without him. Perhaps you need to explore whether some old flame is cooler than he is. Whatever it is you need to do, make sure he sees that your life is going to keep progressing with or without him.