Chemistry (& how to tell when it's there)

Hi all, For those who remember the last two topics I posted on here this is a follow-up issue to those topics. It's regarding a female friend of mine that I had become attracted to over time who, had went through (and is now done with) a messy divorce settlement and is stationed at a deployable unit in Florida (I'm stationed in Mississippi). For the people who may care (which isn't many), what happened with the last topic is that I ended up asking her for an apology for stating that I didn't have any "confidence" when talking about how we wouldn't work out theoretically due to still feeling some hurtful emotions from it, how she used the information I gave her as we were becoming closer friends against me in such an (in my opinion) unfair way. She did apologize but I felt like her tone changed a bit once I brought it back up again (we were on the phone). I didn't think much of it at the time. The conversation went well, neither of us got angry, she apologized, whatever. I call her back later that day (like she told me to) and I don't get an answer. I try again over the next couple days and I still get no answer which led me to believe that maybe she really was upset over me asking her for that apology. Long story short I called her from a fake number, she answered, I got upset due to thinking she was ignoring and avoiding my phone calls and indirectly blasted her on FB through some statuses (I didn't tag her or anything), she saw them, called me out on it and stated that she was going through a lot of stress at the moment with just moving into a new house, getting all her stuff set up, and dealing with a last minute deployment (which she's on now). Basically I was wrong and she was not ignoring me after all, she just didn't have time to talk. I felt like a huge asshole, apologized to her and she said she's over it now so crisis averted for now. With her being on deployment for now I think now is a good time to reflect on how exactly I got here in the first place and what this topic is primarily about. Keep in mind that this female friend is someone who I was able to let my guard down around and be myself around, was never at a loss for words around and when there was silence between us during conversation it didn't feel awkward at all, we both cheered each other up many times when we were going through stuff, I felt like a genuinely funny, charismatic guy when around her due to being able to make her laugh so much and she knows things about me that even my family doesn't (and doesn't judge me or look at me differently for them). I can't describe this in further detail but I FELT (at least I thought) chemistry with her. Was it an issue of her not quite feeling the same way? I just don't understand and am confused. I told myself way back that we got along so well that it just wouldn't make logical sense for us to not be together and that if we didn't that I would break down mentally. It must have been a self-fulfilling prophecy because oddly enough that's exactly what happened unfortunately. But what exactly is chemistry and how do you know when it's really there? How can all those qualities/conditions I mentioned above (being able to relax and be myself around her, mutually cheering each other up, never being at a loss of words, etc) be present and there NOT be chemistry? How will I know in the future when or if I THINK I feel chemistry with somebody else that things won't break down again like they did with this female friend? If things can fail like they have with someone that I strongly and understandably felt a lot of chemistry with then what chance(s) do I have with anyone else? Is there even a point in pursuing anybody else?