It appears that your current situation involves being in a committed relationship with your girlfriend, while this new person has recently entered your life. It's worth noting that the new person might not experience the same level of emotional attachment given the shorter duration of your acquaintance. Generally, people tend to be resilient, and they can adapt to such situations, at least that's how I would perceive it.
Dealing with a heightened libido can be approached in various ways, and it doesn't necessarily have to result in pursuing a romantic relationship outside your current one. You can explore alternative methods to address this issue, such as finding ways to increase your girlfriend's desire, and additionally often desire can be present but not explicitly expressed so she might want more intimacy than you know. Additionally, many couples who are capable of having children choose not to, so you aren't obligated to follow a traditional path in that regard.
Regarding the romantic component in your relationship with the new person, it's a valid question to ask if it was necessary. Maintaining a platonic friendship is also an option, as friends can provide affirmation and emotional support. In most cases, I wouldn't agree to give up close friends for the sake of a romantic partner, although this situation is different since you met the new person after beginning your relationship. However, you can assure your girlfriend that your intentions are not malicious, as you have been open and honest with her about the situation.
