Yeah, you sound like her bitch. Brutal honesty. Have you been fucking this girl on a consistent basis? Why would you feel like you were in the wrong when you fucked the other girl? She wanted to feel power and went 'boo' when she found out about the other girl and it made you jump. There is always one truth when dealing with women...they're jealous as FUCK. If a woman you think is interested in you yet shows no real genuine jealousy, then she cant be that interested.
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we have a really strong connection.
That's some shit that'll wreck a man's love life spouting this all over the place, and it has to in some way convey to your girl. It's a common knowledge that extends far beyond these forums, and it's that women SAY they want this and other gentle understanding traits when in reality they are repelled by this clingy and needy kind of behavior. Do you truly believe that you have her truly have something special? GREAT. That's still no excuse to veer off and not play by the rules of the game. Until you and her are ready to commit (And please be having sex) there isn't any need to attach any strong emotions to what you two have. She has done nothing to earn them besides existing. Maybe make her suck on your dick a little bit and maybe she'll rise through the ranks 
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but i told her it kinda made her look slutty
I was gonna say this big elaborate speech why this wrong but...im sure you figure that out as soon as you said it right? Girls flirting strongly with other guys can make some men jealous, I wont deny or try and change this fact, so decide for yourself how it makes you feel and tell her. Act on it. Your questioning your own feelings for a girl that is doing nothing but leashing you on. Flirting like that in itself is a red flag. Extreme flirts are basically attention whores. Little passing by's with cute guys gives her validation, and it wont stop whether you nail her or even put a ring on her finger. If that's not something your gonna be comfortable with, save yourself alot of hardship and hassle and cut your losses. Im not saying it to be mean, but is one girl who tries so little to earn your attention worth this mental stress your going through? The greatest skill you can learn for this is to recognize and ignore the people who put nothing into relationships asides from themselves.
So from all this, you can assume what my answer to your big question is. My advice is to stop doing shit with her. Hell, never talk to her or text her for a while. Trust me. Call up that girl you fucked from before and ask her what she's doing this weekend. Have fun, be fun. I promise within a month's time this girl will be kicking your door in. She NEEDS your attention, and you're letting her know that unless she earns it, you will not give her what she needs. This is a bloodsport man, not "Strong connections". All men that are truly good with women have this said character trait. Take advice that'll help you be a better man that can make decisions with a straight head. Doesn't even really take years of experience either, just know what's good for you and do what you want without feeling stupid regret from some chick who wont put forth what's asked of her.
She can quite literally go fuck anyone of those guys she flirts with, She's gonna need to get sex somewhere. If you stay quiet now, I refuse to help you when you come back to this forum explaining that situation. I know you want her emotionally, but she's no good.