Help and opinions about difficult PhD choice I would like to share my situation, as I really need to have opinions from people in the academia or people who had similar doubts in the past. I am totally confused about starting a PhD, I have multiple variables fighting and I would like to get thoughts on this.

To introduce the situation: I have a MSc in Environmental Sciences with top grades, and a huge interest for a very specific, competitive, low-founded research topic (topic A). Something I wrote my MSc thesis on and I am totally passioned about, and something I dream to build an academic career on.
I tried for months to get a PhD into this research field, applying to general PhD calls throughout the whole Europe, as no specific ones on the topic were published. Every time, I got accepted in the program, also when the selection was competitive, but I found no supervisors working on topic A or available to invest funding on topic A (“You need to finance your own research”).
During this tiring and time-consuming process, I have not started a proper job, I have been giving financial and personal instability to my girlfriend, whit all the related consequences, and I have been in the worst stress moments of my life. After some months of this torture, I was resigned to give up because of the lack of possibilities. Two choices were left: finding a “normal” (non-academic) job and spending the rest of my life doing something “stable” which I don’t like, or starting a PhD on another topic. I gave myself one last chance, and I decided to apply for an advertised PhD on topic B, a topic which I don’t feel involved with, but “still better than a normal job”.
I passed the first selection step for PhD B, and I will have the personal interview on Feb 21st. I am likely to win the position. My girlfriend is happy, they would give me a lot of money and she likes location B.
BUT suddenly, a few days ago, I received an email from a friend with a freshly published PhD position on topic A, in a university in a location A on the other side of Europe. My heart stopped, I think I had a shock. I don’t know how to explain it to you, the probability for a position on that specific topic to come out were so small that this seemed to me more like a miracle. The required skills were perfectly aligned with my abilities. It was simply my position, it was me.
I immediately applied, and I wrote an email to the supervisor introducing myself and explaining my passion. I got a reply after one week, saying “your general background sounds good, you can express your passion in the cover letter”. Good. Maybe.
Now, I am totally stuck with my life. The deadline for applications for topic A is Feb 15th, and the position is starting in May. This means the selection process could take until April. But I will probably get the offer about topic B at the beginning of March. I have no time and money left to look for other possibilities, I need stability somewhere for some years. I would like to bang my head against the wall.

Possibility 1: I accept PhD B and I move all my life to location B. If they offer me PhD A, I say no for the sake of honesty towards supervisor B.

Possibility 2: I accept PhD B and I move to location B. If they offer me PhD A, I move again after one month, feeling extremely dishonest towards supervisor B and guilty towards my girlfriend to always make her life stressing for my own selfishness.

Possibility 3: I refuse PhD B with the hope to get PhD A. I don’t get PhD A. I start a normal job, end of the story.

Possibility 4: I refuse PhD B with the hope to get PhD A. I get PhD A. Ideal option. The point is here I have actually no idea of my possibilities to get PhD A. I am really a perfect candidate, but I expect a lot of people to apply, and I have learnt through experience that some positions are just assigned from the beginning, for example. Furthermore, I don’t want to annoy supervisor A with other emails.

What would you do in my situation? I need advices, thoughts, insults and everything you consider useful.
Thanks in advance.

Nebbiolo
Some general points I will address.


It is much easier to get a PhD in one topic, obtain a faculty position somewhere, then pursue a new niche field of research, than it is to obtain a PhD in the niche field in the first place. I did a dissertation on a topic I am not passionate about. But I was passionate enough about it that I could spend four years thinking about it then move on. In my current position, I do not do any research on my dissertation topic. I have shifted towards something that interests me more. All of this was facilitated by the fact that I already have a PhD. I can control my funding and research much more now that I have a PhD. 
This is based just on anecdotal evidence, but I have found that students who want to find a topic they are extremely passionate about usually end up unfunded and take several additional years to complete their degree. And often, in the end, they end up writing a dissertation on a topic they are not mind blowingly passionate about. 
If it is stability you are looking for, topic B may be where you need to look. You will need to decide between pragmatism or passion. 
Be aware that if a field is extremely niche right now, it likely still will be in ten years. This means that funding and opportunities will be harder to come by if you pursue faculty positions after getting a PhD. Unless it just happens that somehow your topic all of the sudden becomes in massive high demand, niche subjects tend to sort of stay just that: niche. 
I cannot give you relationship advice. But if you are going to be in a relationship, her feelings do need to be taken into account.