Hey, good to hear from you again.
I have been thinking a lot lately about my patterns in relationships of late.

My ex's birthday was yesterday and I fought the urge to break no contact and wish her a happy birthday. Part of it was the desire to respect what she told me was the reason for ending things and to not speak for however long but in truth I was afraid of being left "on read" or have a short superficial conversation. I feel relatively ok about it today even though yesterday was mental torture
What's it like to reflect on Sunday being mental torture and Monday feeling OK-ish? Anything stand out to you?
I still miss her a lot but I am starting to wonder how I would even feel if we talked again in the future or even met up.
Yes, this is relatable. This seems like a normal part of the process of grieving the end of a relationship -- holding both of those feelings at once.
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OK, on to the reflections on relationship patterns:
I often look at other women I have had close relationships or dynamics with. I start seeing borderline traits in all of them looking back but it is unhealthy for me to start self diagnosing many or all of them as having BPD or at least traits of them.
That's a good question.
One thought is that if a person looked back on many relationships and decided to label the partners as "disordered" or "abusive" or whatnot as a way to avoid personal responsibility, then yes, that is unhealthy. In fact, that can be a

to us: does a friend, potential partner, date, etc, label most to all previous relationships as "abusive" or "toxic" etc, AND hint/imply "but it wasn't my fault"?
It can take some nuance to thread that needle. I think it is possible to be a person who, through childhood/early adult experiences, "got wired" to be attracted to certain vibes/traits/etc. So, yeah, it's possible to have a string of previous relationships that yes, might mostly or all qualify as "BPD-type".
The big question though is what the person does with that information. To go in the direction of saying "Seems like they all had BPD or BPD traits... but it wasn't my fault" is in itself a

about the speaker. To go in the other direction, though, of saying "Seems like they all had BPD or BPD traits... so what can I learn about myself from my choices, and how can I use what I've learned to be healthier" -- that's not a bad thing, that's not unhealthy.
I tend to get involved closely with women who have emotional trauma and/or mental health issues. I know the simple reason is why because of my own mental health issues.
And it sounds like you're willing to take responsibility for your part in participating in those relationships. That does not sound unhealthy to me. It sounds like the start of some reflection, learning, and having the opportunity to take a different (though perhaps uncomfortable, at first) path moving forward.
I wonder if I could even be in a relationship that was healthy if the person did not have some level of trauma in their background. That expression, find someone who matches your own level of crazy.
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That's another good question. I think the answer is going to be tied into your view on if people can grow and change. I think it's possible to make choices that long term "rewire" your desires and attractions, through working on understanding how you got to be you in this position. Or, actually, sort of arguing against myself, I think it's more that you can decide to make conscious choices, regardless of for whom you feel that magnetic attraction, about who you want to be with. I think you can choose stability/health in a partner even when part of you might say "but what if I were with this other person instead, she's so magnetic/charismatic/exciting..." Maybe that's the growth -- taking that subconscious attraction that in the past has "run the show" and instead realizing that you can make conscious choices not to act on it, to choose different partners.
Anyway, food for thought.
Another way to look at it is -- even if it may be true that right now, at this moment, you might still choose someone with trauma in their background, that isn't necessarily a "life sentence" for you. Think about where you were at even a few weeks ago. I hear a difference in "you now" from "you then". "Future you", if you choose to put in the work, isn't destined to more disordered relationships.
I suppose my ex has made me question a lot about my life up until now and what I want my path to be going forward.
Yeah, I definitely hear that in your post. This is a good place to come and just get stuff out "on paper" and think.