The problem you made was not being forward or assertive enough. She was basically saying you just wanted to take advantage of her and have sex (via friendly tone) - whereas the other guys just DID, and she was totally up for it. That's the difference. She was saying to you - and doing to them.
She already knew you, and probably viewed you as safe and unsexual. So, as you were talking - she said you just wanted to have sex with her, or whatever. Whereas, the other guys likely charmed, seduced, flirted, and escalated sexually. She didn't say **** - because they just went for it, and didn't act friendly. Sweeping her off her feet, if you will. She knew what was up, and how to define them. And she was totally up for it - probably not even thinking about it at the time. They were viewed as sexual, aggressive beings - and you weren't.
You have to advance through actions, and set the sexual tone early. Then play the game from there. There's a difference between being friends and lovers. Quite a big one, actually. Being confident, assertive, sexual, and NON-friendly has a lot to do with it. You have to just go for it, and present yourself as dating material - not talk, act friendly, listen, remain passive and attentive, always being available, the shoulder to cry on, whatever. That's how FRIENDS act. And people generally treat you as they view you (based on your behaviors).
Acting like a friend for 3 years (as an example) while they're dating someone else isn't going land you in the romantic zone once they break up. Quite the opposite. You'll STILL be viewed as a good friend (as you were behaving), and be passed up in favor of a complete stranger. Happens all the time - hence the "nice guy" whining that goes on everywhere.
DON'T ACT LIKE A GOOD FRIEND. A distant, casual one, sure. But don't be the super-close confidant, or focus on them - while they're dating someone else, and having them SAY you just want to have sex, or whatever. Bad, bad idea, and not where you want to be. And that's an indirect friend-zone rejection, anyway. They should be horny and intrigued, and WANTING sex, and viewing you in such a manner.
But the big thing you'll notice is that her words don't match her actions. She said she knew the ex for however long before dating him; you pretty much followed suit, thinking it's what she wanted; she said you just wanted sex, you held back; she went and had just sex with other random guys.
See the LACK of connection, here? It doesn't add up, and contradicts itself both times, because it's all crap. Words mean nothing, and it's especially bad if you hear them through friendly conversation. Never base your behaviors around their words, or you'll end up confused and disappointed (and possibly heart-broken) when they don't match their actions (ie, all the time). And this **** is very common (again, nice guy whining). They say one thing, and do another. And you're left wondering WTF is going on.
Don't assume these guys are just using her, and she's having her fun. She's dating around, sleeping with these guys, and will end up getting involved with one of them. This is common ****. You're FZ'd, and she's doing her thing, and passing you by as a non romantic prospect. Just like when they say they're confused, afraid, not ready, or not looking. They're not "waiting" or holding out for you before they settle down. These guys they date aren't strangers, and you're the one they're waiting for - because they know you so well, and can trust you, and blah blah. In fact, that's why they AREN'T attracted to you, and date all these other guys instead. You're just a good friend. While you sit here waiting - she's going to keep dating other people forever, and end up getting involved with some of them. That's how it works. The only one waiting or stopping is YOU.
The entire tone of the relationship should be sexual in nature. Not that it can't be friendly as well, but there should be sexual inneundo's and hints of what they want you to do to them, flirting and touching, teasing and complimenting, wanting to see you in a romantic sense (ie, missing you)... You can just tell when someone is interested in a romantic relationship, or that you are in one. And, when you aren't. None of this wondering, mixed messages, looking for tell tale signs, and making things bigger than they are bull****. You'll know.