I've been living with my GF for 5 years, eventually I discover that attraction to her did disappeared like 1 or 2 years ago. After all some studies demonstrate that ~2-3 years within a relationship, attraction tend to end.

But apart from attraction, thing is that now my GF wants a kid, she has that age when, If she don't go for a kid, she may never possibly get a kid, and I am a little bit younger than her and not so sure of having a kid yet, but she starts putting pressure in the topic and starts to disturb me seriously. I would like to have kids maybe later, but not being realistic enough, this girl needs to go on now or never, so is kind of stupid from my point of view having this idea of leaving it for later at this point. If I refuse now to have kids, she may dump me soon.

I met my GF like 6 years ago, we moved after 1 year of dating and the thing is that 6 years ago I was in the PUA community. I met multiple other girls before, but at some point I felt this one was the best that fit me in terms of advancing into a more serious relationship, thats why I left the PUA community

Problem is, that lately I've started dating another girl, like 2 months ago (I know, is cheating ). Now for some reason that I know her deeper, I'm starting to feel she has in general terms, better attributes (attraction of the beginning may interfere in an objective way of reasoning).

This is the thing: Switching girls, may lead to me on finding a better girl in the future, more time to have the opportunity on the future to have kids with her or whatever it leads this.

Bad Part: Leaving my girl, in this point makes me feel bad in two senses: More or less I knew that this day will arrive late or soon, so I asked repeatedly this question: Why I did not dump her before so she had more time to find other guy to have kids and that? Makes me feel seriously selfish, but now with the idea that there is a new girl that is possibly better than my actual GF, makes me feel confused (but maybe are just passing feelings that are not really true, due to the shortness of the relationship with the new girl).

I don't know if the community has experience regarding this type of emotional/relationship disarrays, but I would like to hear some advice on how to put a little bit of order in my mind.

If you are thinking about why you didn't leave your girl earlier than it's already a lost cause. You are cheating on her now. If you leave her asap you are doing her a favour. Yes she will be hurt. But she won't be half as hurt when she finds out that you've cheated on her later on.
So my idea is, dump her as quick as you can. And stay strong not to go back to her.
I've been in your situation so I know how this feels.
Besides she wants a kid. You don't. This is big difference in terms of your future plans and it will ruin the relationship eventually.

Thank you for the advice
This morning I have talked with her, and we have decided to split as soon as possible, at least temporary
(I've read your advice after doing this by the way, but anyway it makes a lot of sense to me)
Really sad situation for both.
Can't understand how can things be screwed that much, this is life i expect