I have found that I actually do NOT get along at times with the signs that I'm supposed to get along with. Me being a Libra, I should get along well with Gemini....but I don't (at least not with Gemini women: I don't know as many Gemini men but that said I've never been close to any/good friends with any Gemini men). Usually I get along with Gemini for awhile but then there's one fight in the relationship and they end things with me, even if the argument is minor and not worth ending things. I also have had rough patches with Leo men. Most of my "inner circle" is comprised of earth and water signs.
I also don't believe that air and fire necessarily get along better. Air and Water are both "abstract" sorts of people and Fire and Earth are "concrete" sorts of people (see Liz Greene for details) so sometimes I feel like I get along better with Water (except Scorpio: for some reason unfortunately I usually end up not having good relations or connections with Scorpios...although when I do find a Scorpio that I really "click" with, it's pretty great).
I also feel that any two signs can work together if a) other planets/positions in the chart are good and b) the couple loves each other enough--and understands each other enough--to work through it: if both people work at the relationship and make it a priority, there's at least a chance of it working. I kind of feel that instead of using compatibility to avoid certain signs, it's better to study all of the signs and try to make things work "within the sign" (i.e., using the information about the other person's sign to make things more balanced and harmonious instead of not giving someone a chance just because your sign isn't traditionally compatible). To be fair, I can see avoiding one or two signs that you really can't stand...but on the other hand someone's sun sign shouldn't prevent you from giving that person a chance. Plus, even if they are a sign that you don't get along with, the rest of their planets may be in signs that you do get along with...or else they might manifest the more positive traits of their sign. That said, one of my favorite signs in the zodiac is Capricorn, which is supposedly my worst match. Capricorns have, with only a few rare exceptions, always been great to me and very kind. I feel like we balance each other out: Cappies help me mature and be more responsible and I help them relax and see the beauty in life. One of my most trusted friends is a Cappie and she is very sweet and loyal. I also like Pisces most of the time (again, even though we're not supposed to get along).
I'm wondering if my other planets have something to do with it. I have:
Uranus, Saturn, ASC=Sagittarius
I've also had difficulties with Aquarius: as much as I like them, they don't usually stay around long enough for me to get to know them as well as I would like--and usually when I meet an Aquarius I went to get to know them so this is frustrating!