Probably the clean break is the best…but that being said, you mentioned she was in a play which tells me that she enjoys drama.
When I was in the dating scene and wanted to break up, I used to try to work it so the woman got the impression that she was the one who broke up with me. I always felt it left her with a feeling of being in charge and made her feel better about the whole thing.
There is the simple direct method - "I can’t take it any more. You’re thinking about leaving me aren’t you? I’ve seen the signs before and I don’t want to draw it out. Don’t lie, I’m stifling you, I lack your creativity, I’m shallow. I admit it. You’ve got all that stuff and I don’t. But I’ve got enough self-respect to leave a relationship before I am asked to leave. So good bye.
There is also the “I’ve found God” break. When she comes home from rehearsals and finds you on your knees with a number of people in a prayer circle, she will start thinking, “What have I got into?” Especially if you ask her to stop spending so much time with sinful “theater types.” Or what ever sinful “type” she might have been out with. There is the addendum to this - the religion you turn to could be offensive to hers, ie, if she is Jewish you turn to radical Islam, if she is Catholic, you find the Rev. Hagee interesting, etc.
There is the already alluded to paranoid type that can run off significant others. She gets a phone call and after she hangs up, “Who was that?” “You’ve been getting a lot of calls from a specific man haven’t you?” I’d like you home sooner after work," “You don’t look at me like you used to.” “Who have you been spending time with?” ---- This one has been known to backfire, however.
There is always the, “I think I may be gay, and I need time away to find out.” This can also backfire with the clingy type.
All of these require a certain amount of subtlry and finesse, which after reading your OP, you may not possess. The clean break is probably the best.
Finally there is the ploy of just leaving the computer on to this thread when you know she is coming into the room to use the computer.
Oh, you did that this morning?