Whether you leave your partner for someone else depends on your value system and, to a lesser extent, your definition of love.
The only time someone else other than your partner would even look like the “right” person is when your current person isn’t, as defined by the above. Either they were never “right” or at least one of you didn’t build and foster and commit to the relationship, but either way. There is no “right until proven wrong,” “right until better right comes along,” or “forever until I change my mind.” If they suddenly seem replaceable, it’s because part of your heart always thought so.
This also means you almost certainly chose your partner based on other measures and values.
And what you do with meeting someone new really depends on what those measures and values are — how you view relationships, partners, people, and love. The “right” person is going to be someone who best aligns with you living your values.
If you’re someone who values tradition and security most, the “right” person is the one who best fosters this in the long run.
If you’re someone who values status most, you’ll choose whichever person offers more.
If you value harmony, the “right” choice is the one with fewest hurt feelings and least disruption to the peace in your life.
If you’re someone who sees life (and other people in it) as fluid, you may not see partners as static, one and done, til-death-do-us-part commitments, but rather companions in life to the extent that it’s mutually enjoyable, and in that case the “right” choice is whichever one that supports your personal journey.
If you’re someone who simply values connection and sees love not as “romance” but as a daily decision, you’ll choose the person who makes that work feel most like a labor of love.
And if you’re someone who values your specific partner (and your connection with this specific person) most, you wouldn’t be incentivized to build a competing connection with someone else. Nothing else would stack up — even the temptation of attraction.
I know what I would do. My guidance to anyone else is the above.
But regardless of what choice is made…
If you operate from a place of love, you’ll make the decision easily — and honorably.
If you operate from a place of fear, you’ll do it poorly, or in despair.