To people who are shallow (or in my opinion, people who are shallow) tend to see 3rd party in the following scenario:

A and B are an item. C comes along and then all of a sudden, A is together with C, and this to D is a clear cut 3rd party case. WTF???

Who the fuck is D to judge if it is a 3rd party case?

Does D really know what happened in between? Do A and C and B for that matter owe D any explanation? Is it fair for D to judge, even though D has experienced some personal 'tragedy'?

'Oh, I'm the victim of a 3rd party case so I detest all whom I think is a 3rd party.'

Sorry lor, your sad story touches my heart but that's about it, get over it.

How can D be so sure that at some point in time, he/she is not a 3rd party in some sense? Are you very sure that you are not the cause of breakup between your current partner and his/her ex?

'Oh, at least he/she broke off and had a 'clean' break before we are together.'

Sure, everyone says that.
How long was the breakup before D gets together with his/current partner? How can D be sure that he/she is not one of the reasons they did not even try to work things out in the first place? Self justification is such a pathetic thing.

Now consider this:

D for some reason does not like certain members of the current partner's family and keeps silent during family gatherings, often causing awkward silences. The rest of the family continues converations and generally having a good time and D felt left out.
Thus, D often have fights with the partner, accusing of being left out and the partner talking to people D does not like.

And apparently, D does not give a damn of the awkardness he/she is causing the family due to his/her choice of keeping silent in front of the so called 'people she dun like' To D, it is ok cuz he/she is being his/her 'real' self and not 'acting' to be friendly when he/she dun feel friendly.

Now let me ask a stupid question but it seems pretty obvious to me that D is now the 3rd party right? Maybe not in the strictest sense but well, D seems to be causing quite a disruption in an otherwise 'harmonious' situation mah.

Moral of the story:
To people like D, pls fucking grow up. The world does not just revolve around you.
There are many things in life that are not to your liking or against your so called 'morals'.
So? Get over it.

You may choose to be indifferent or think that you are right in doing the things that you are doing, that's not wrong but do pause for a moment and think if you are being selfish for not considering the feelings of those around you.