most people pretty much accept the idea that if you do something that might be hurtful to someone if they found out, and they never find out, then it's not hurtful at all
but personally i think that's pure hubris. Life isn't so straightforward. All i can speak on is my own life really, but i know that if i commit to one thing, i'll end up usually doing another, and it'll be even better. I'm not talking sexually just with projects. But also sexually. Do you really wanna be with this person? because if you start down this path, you might find someone you hook up with to be way more than you expected.
Honestly i think life has a way of playing dialectical jokes on us. What I predict happening: you have a ldr gf, it's really good, it's serious, but there's no sex. So you go fuck some people inconsequentially, because you just want sex. This very lack of meaning opens up the space to breath, whereas a "serious" relationship can be stifling and full of respect and care (i.e. full of insecurities because you respect them too much, full or trying to not step on the other's toes because you care so much), and when you see what can blossom out of a "no strings attached" situation, you leave or grow distant from your old gf. Now this new side thing is your main focus, but it can't last because it was formed by cheating. This leaves both sides with insecurities, and maybe there were feelings there that covered up the fact that you two don't actually have as much in common as you thought. Now you're alone, and free to fuck whoever I guess. And if you're smart, you'll be able to be friends with people without getting too close to the people you really love again, or getting too distant in your closeness.
It's like chemistry, but then again not really because in chemistry a stronger bond will take priority over a weaker one. Whatever
The point is, if you love her, she needs to be your side-slut. There can be no other side sluts above her. If you want to cum, use your hand or sex toys.
The problem here is a fundamental misidentification of what a relationship is, imo
The primary form of relationship is side-sluttery
everything else is secondary. You've accidentally put your woman in a secondary position, and you're looking for a new person to fill that gap. You need to make your gf a slut u fuck, and take it less seriously so that the idea of "just fucking sluts" can't seem like a minor thing on the side, but as an equal relationship to your established one, making it more consequential, how it really it. This idea of a serious, normal, "full" relationship, opposed to a half-formed, temporary, "just sex" relationship is wrong. It's cope to cover the fact that they're really on the same level, and you could seriously threaten your serious relationship with a (seemingly) temporary, sex-based one.