3yrs is right around when the cupcake phase ends.

Congratulations, you've now entered the steady, sometimes monotonous phase of "comfortable".

In the comfortable phase, you have to work to keep a relationship from feeling stale in the absence of the novelty of the cupcake phase.

But honestly? You sound like you only "like" your gf, and that doesn't bode well. Even in the comfortable phase, you should still have some semblance of excitement. I mean, you're still getting to have sex with her. The woman you've decided to be with.

My partner and I have been together for 5+ yrs, and we have a little one so there's not a whole lot of room for "super crazy hot sex". Our first three years were full of it. But now? We're tired. Life's crazy. Our child is the ultimate mood killer. But, even when we're just having maintenance sex, we're still happy and excited to be able to still share that sort of physical intimacy (even when it's 10 minutes of silent grinding so we don't wake the sleeping monster). And when we can, we spice shit up. But it takes planning, and effort to break the cycle of maintenance sex.

If you're genuinely feeling zero excitement towards having any physical intimacy with your partner, and you don't feel lucky to have her, then it's time to move on and let her go. Especially if you feel lust for other women but not for the wonderful kind woman who you've grown bored of. It happens, but try your best to be decisive.