Hi Volleyball26 and

You're not alone in feeling guilty, sad, or obligated about your child's other parent falling short. Other members here have experienced that, too -- kind of a grief that their child isn't getting the other parent that they ought to have.
Sounds like there are a couple things going on. There's the purely logistical/scheduling side, and then there's your emotional experience.
Logistically, just a few questions:
how old is your daughter?
how long have you and her dad been separated (or divorced)?
is there a formal parenting plan in place, or is the current schedule an unofficial agreement?
does he actually have a job where he truly works only weekends?
how do the two of you communicate, if he doesn't have a phone?
is he diagnosed with BPD?
...
The emotional side of parenting/stepparenting when BPD is in the mix is huge. My husband's kids' mom has many traits of BPD, and she is married to someone with many NPD traits. Feeling like something is our fault, even when we know intellectually that it's not, really rings true to my experience, too.
Persons with BPD/NPD often have poor, weak, or unhealthy boundaries, especially around emotional responsibility (my feelings are my feelings, your feelings are your feelings). Many pwBPD also struggle to manage their overwhelming and rapidly changing emotions in healthy ways. Blame, whether subtle or explicit, is often a feature of BPD-related conflict. BPD is a shame-related disorder, so when you put together overwhelming inner shame, few or no tools to manage the feeling of shame, and poor boundaries, that can lead to situations where the pwBPD uses the "tool" of blame to manage feeling shame. That can be "on purpose" or not... but in a way, it doesn't really matter, because the issue isn't whether they "meant to make us feel" something, the issue is -- we're feeling something at odds with what we know.
I'm curious about what your relationship was like when you were together. There are many frameworks for looking at relationship roles, especially in less functional relationships. Sometimes, one partner is in the role of "victim" or "needs rescuing" and the other partner is the "hero" or "rescuer". Both partners get something out of that. Or, one partner is the "designated patient" with "issues", and the other partner is "the healthy one" or "the functional one". Sometimes one partner is deeply dysfunctional (alcoholic, for example), and the other partner finds meaning and purpose in "covering up" for that partner. There are many more frameworks and roles for relationships, so these are not all the possibilities.
And, if you want to dig deeper, we often enter adult relationships having been "trained" by our families of origin about what "normal" looks like... and sometimes, the lessons we learned in our FOOs weren't all that normal.
Understanding what roles you took in your relationship, might shed some light on these residual feelings you're having, now that you're out of the relationship.
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Feel free to keep posting and sharing, we'd love to hear more of your story!
kells76