So you find yourself in a community show, and naturally in a few short weeks, sporadic, brief rehearsals evolve into nightly work sessions, (or ordeals) often lasting for hours on end. The closer one gets to the debut, the more tension there is. As well as more pressure and excitement.
Add to this the things from your life during the day that you bring into rehearsal. By the end of the night, the result as often as not is a highly charged, smoldering kettle of emotional soup. Just as frequently, there is someone else, who is working on their own emotional home brew during rehearsal. When two such people catch each other's attention back stage, something I call incastutation can take place. (Infatuation, with a cast mate. Clever, right?)
This is of course, human nature; attraction due to mutual difficulties with an outside situation. Theatre experiences tend to heighten this already acute programming in our minds. (Rare has been the play I have been in where this did not occur to some degree to someone.)
I blame the off stage drama, and the fatigue, and the excitement of the stage, and any number of other variables. Whatever the cause of it, the temptation to pursue such interests can become quite strong at times, understandably. Sometimes things can get pretty serious. But let's face it; that is not always good for your performance. (Falling "in love" and performing well are very difficult things to keep one's mind on simultaneously.)
And if things get serious and then go sour before the show opens...It can be less like an opening night, and more like an opening nightmare.
Just take it slow. Much slower, in fact, than you might otherwise take a budding "relationship." Stay friends during the run. You owe that to your cast mates, and the production. Remember the old adage "attraction means distraction". If there is anything there between the two of you, it will certainly be there after the show closes, and you can makes each other's heart flutter as much as you like. If not, imagine all the crap you spared yourself, and everyone else involved.