I've recently started seeing an already established couple, my first time doing any sort of poly stuff. While I like both of them and don't mind being sexual/affectionate towards Person A, I really only want to be in an actual relationship with Person B. Idk how to bring this up without it seeming like I dislike Person A. I just feel like Person A and I don't mesh super well romantically and if we tried to actually date each other then I'm worried it would end badly, and I don't want that to happen because I like Person A as a friend and don't want to lose them or Person B.

This might turn out to be a non-issue. If you’re okay being sexual and affectionate with Person A, and that’s the kind of relationship Person A wants with you, then you’re all on the same page. Whether you feel like internally labeling it “an actual relationship” is less important than whether what you’re doing is working for everyone.

You say that “if you tried to actually date each other then…it would end badly,” but also that you have “recently started seeing” them - so maybe you’re overthinking this, and the way you’re currently relating to each other is working fine. You’re anticipating a change (from whatever you’re doing now to “an actual relationship”), but why do you think that change is necessarily going to happen?

The best way to figure this out is to ask both people, probably during a handful of low key conversations, both one-on-one and together, what they want and expect from you. Are they envisioning a “balanced” situation where you’re dating both of them as a unit, or are they okay letting your relationship with each individual develop in its own way? What does Person A expect from you?

Hey I've been doing some research (I'm new and still questioning) and I had an idea that I think would be more sensible than trying to add a third person straight into a couple and would like your opinion (please). My idea would be to have one person of the couple date the potential third person for a while and then the third person could start dating the other member of the original couple too before the triad is formed. I thought this might help reduce the stress on all involved but idk.

This kind of arrangement doesn’t really work, because it puts all sorts of prescriptions, demands, and expectations on the “third person” to date the other partner if they like one partner.

Think about how hard it is to find someone you ‘click’ with - someone you enjoy dating and want to be in a relationship with. Now imagine that you’re dating someone, and they go “also, as part of a PACKAGE DEAL, when you date me, you also date this other person! Who you didn’t get to choose, they’re just also here!”

It puts a lot of pressure on the “third” to like this other person. Even if you say you want to “take things slow” or “let things be organic,” there’s a major expectation there that “once you’re ready, you’ll start dating this person too!” What if they’re never ready? Most people I meet are not people I end up wanting to date. Simply being a partner of one of my partners doesn’t automatically make someone a perfectly eligible candidate for me. 

Almost no one likes being told who to date; there’s a reason arranged marriage is no longer in vogue for the most part. So this isn’t a very realistic plan, I’m afraid, since it requires someone essentially assigning a partner to someone else.

Ultimately, relationships are healthiest when they form organically, not out plans, arrangements, timelines, or prescriptions. If three people want to all date each other, let that happen. If it’s ultimately healthier and more sensible for a V-shape to form, well, it might be better to make that work than to try and force human relationships into an arrangement they’re not well suited for.

Think about this from a statistical point of view: You are looking for a “closed, three party relationship,” which means you need someone who is:

Physically attracted to you

Physically attracted to your partner

Physically attractive to you

Physically attractive to your partner

Intellectually interested in you

Intellectually interested in your partner

Intellectually interesting to you

Intellectually interesting to your partner

Sexually compatible with you

Sexually compatible with your partner

Emotionally engaged with you

Emotionally engaging to you

Emotionally engaged with your partner

Emotionally engaging to your partner

Lesbian 

Polyamorous

Interested in a closed triad

Consider how hard it is for straight monogamous people to find someone to date - it takes most people way longer than six months to find someone. And they have it easier, statistically - they only have to find someone:

Physically attracted to them

Physically attractive to them

Intellectually interested in them

Intellectually interesting to them

Sexually compatible with them

Emotionally engaged with them

Emotionally engaging with them

Straight

Monogamous

So you’re up against two numerical challenges:

One: There are just fewer poly lesbians interested in closed triads than there are straight mono people trying to date. No matter where you are, in this day and age, straight people looking for a mono relationship make up the numerical majority.

Two: you’ve significantly increased the number of requirements for compatibility. Now they need to be into two people and two people need to be into them.

So, from that perspective, six months is not a long time to be looking at all. 

From another perspective: think about the approach you’re taking. You don’t really “add another person to your relationship” - people aren’t sex toys you pick out with your partner together to spice things up. Imagine reading a dating profile by a person saying “I am looking to add a girlfriend to my life” - would you want to be a thing added to their life, or would that perspective and phrasing put you off?

Think independently, and talk together, about why you want to shift your relationship this way, why it’s important to be in a closed triad, what you have to offer people you date, whether you two as a couple form a “unit” to date another person and how that impacts your expectations, etc.