Been a while since I've been back on this site!

Well, my friend and I went for it. Being in a serious relationship I mean.
And it's been... an interesting couple of months to say the least. Interesting enough that i find myself coming back to this forum and this thread looking for advice if that tells you anything.
My friend-now-girlfriend and I have been having some serious issue over the past month or so and I'm really trying to think over what would be best for the both of us. I care for her deeply, and I want her to be happy. Thing is, I want to be happy as well. And while I don't mean to imply that being with her makes me unhappy, lately I've been thinking if we might not both be better off if we were again friends.
Again, I don't want to send the wrong message. I really, really, like this girl. And when we click, we click! It’s gross, really, how much of a power couple we are when things are working between us lol.
But there are a number of things I’m concerned about:

-The sex thing. IDK if anyone will recall, but I have struggled with my sexuality my entire life. This is been an ongoing journey of many, many years. And I expect that journey will continue for many, many more. My girlfriend is the first person I have ever had any kind of sexual contact with. And while I’ve progressed from absolutely freaking out of any kind of sexual contact to general being OK with sex stuff. I honestly… don’t care for it all that much. It doesn’t always send me spiraling into depression, anger, or self-loathing like it may once have done, but even in my best moments, I just feel like I could do without sex. Or at least, sex to the degree and frequency that my girlfriend wants it.
We have not yet done the actual deed, that is to say, we have not yet had intercourse, at my request, as I do not yet feel ready to take that step. We have, however, tried quite a few things short of that. Thing is, we do that a LOT. Like, every time we’re alone together. And I honestly don’t think I’m comfortable with that. I feel I’ve made a lot of personal efforts to make her happy on the sex front. I’ve done a few things for her that I usually wouldn’t be all that into. And I feel like that goes unappreciated.
Sex is important to my girlfriend. It’s a big part of her life and a big part in how she expresses herself and her relations and feelings for other people. She’s been incredibly respectful of my decision to hold off on actual intercourse, but all the same I can tell it’s frustrating for her.

As I mentioned in my original post, my girlfriend has made it quite clear that she is ployamorous. And again, this is not something I am against in the slightest. However, she is in a near constant state of back-and-forth on whether or not she’ OK with me being her sole partner. One day she’ll be totally OK with it, the next she may spring on me that she is feeling confined and miserable with only one partner with whom she cannot have intercourse with. Neither of us knew how this would play out if we got together, and it’s still an unresolved issue months later. At times it feels like either we can be together and monogamous and she’ll be miserable, or we can not be together and she’ll be free to embrace her ployamorous lifestyle and express herself the way that comes naturally to her. I don’t see too many other options. We’ve both expressed an interest in seeing a sex therapist about this topic. And while that’s a nice idea in theory, with both of us currently enrolled at different colleges, it’s a bit hard to put into practice.

-BPD. I have also mentioned that my girlfriend has borderline personality disorder, among a cocktail of other very unpleasant mental/emotional conditions that she’s dealing with at the moment. I have always, even before we officially got together, made it clear that I am available for her. I want to be there to support her, cheer her up, and help her out. But, as I also said before, at times it can feel like she exploits this. This hasn’t changed. If anything, it’s gotten worse.
When I went to visit on weekend, I found myself on an absolute rollercoaster of Mad vs. Angry, Content vs. Upset, Pleasant vs. Aggressive. One moment she’s hugging me and expressing how happy she is that we’re together; the next she’s snapping at me and saying things like, “We were a better couple before we were a couple.” Then, it’s right back around to happy again. And on and on it went.
This is my first serious intimate adult relationship. Her actions were confusing to me, and a bit scary if I’m being honest.
For example; my girlfriend can be a bit… pushy. She’ll ask me to do things that she could very easily do herself such as feed/walk her dog, take out her trash, go grab this or that from somewhere that’s simply a room away. You get the idea. I grin and bear it, usually not thinking much of it. But this was particularly bad during my most recent visit. As we got dressed to out to eat, she gave me this disgusted look at what I was wearing (Simple tan shorts and a light grey t-shirt. Nothing offensive, I promise you) and then asked if I was really planning to wear that. I said yes, of course I was, this was a casual outfit I wore quite often, so I was a bit baffled that this was an issue. She then proceeded to explain what my sense of fashion was deplorable, told me why it just didn’t work, and angrily berated me for not being sensible enough to see why the outfit looked stupid.
Perhaps I was in the wrong, but after completing many, many menial tasks for her without so much as a ‘please’ from her or a word of complaint from me, I felt the need to put my foot down. I told her this, upon which she became extremely sullen and bitter, expressed her need to have some alone time, which I granted. When she returned she was in tears. She weepingly told me that she felt I was disrespecting her and her feelings by not wearing what she wanted me to wear. I was pretty taken aback by this sudden emotional shift; I was confused as to why she was so upset. I politely told her that I did respect her feelings, very much so, but that did not mean she got to dictate which clothes I wore.
…upon which she rose, locked herself in the bathroom, and proceeded to draw, thankfully not actually inflict, cut marks on her forearm.
Did I mention that this is my very first relationship? I was terrified that such an escalation had occurred over me picking out my own clothes. Many hours latter we talked things over and we both calmed down a bit. All the same, I was rattled.
This happened a few more times over the course of my visit, though thankfully to lesser degrees. All smiles and happiness one minute, all bitterness and refusing to talk to me the next.

I feel as though I am constantly walking a tightrope between respecting my girlfriends feelings and wishes while at the same time maintaining respect for myself and standing up for me. And I hate feeling this way.

I honestly don’t know if anyone will bother to read this rant (if you do, thank you very much XD) and I certainly don’t expect anyone to have a magic solution to my problems.
But I have nowhere else to turn to talk about my issues.

I care, deeply, for this girl. I want her to be happy and safe and I want her to smile.
But I’m beginning to think that we might both be happiest as good friends. And we are very good friends. Hell, she’s one of the best friends I’ve ever had.
I knew at the beginning of all of this that she was too important to me as a friend to risk losing. And right now I feel like of we continue like this, that’s exactly what’s going to happen.