Her need for security CAN be filled by a man. Just not this one.
And I don't think she's scared of sex. She's human, she wants it too. She's just scared of his feelings not being strong/serious enough for them to be sleeping together. The guy loves her enough to be with her for 2 sexless years, yes, but obviously he doesn't love her enough to be able to tell it to her and to promise her that he'll still care even after the sex. That's what worries her. And within reason. Neither of you are really sure about this relationship... The issue isn't even about her abstinence here. It's about your emotional incompatibility. If you two were really compatible, love and sex would've come naturally, within the first weeks/months of your relationship! To still be trying and forcing yourselves after 2 years... is just wrong, ridiculous and a waste of time.
And what's this about her being manipulative because she's "waving around the idea of sex" for 2 years? We could say that the guy has been waving around the idea of love too... One isn't more innocent/guilty than the other. Both are at fault, both want their needs fulfilled, and both have been patient enough to still be sticking around only if it's only to get what they want from the other. One thing for sure is that it's as hard for him to not have sex for 2 years just as it is hard on her emotionally to be a in an uncertain relationship. Torture for both.
What I think is that your feelings for each other can't and won't grow any more than it has during the last 2 years... coz after all this time, if he still can't say with certitude that he promises that he loves you (and finally bang you), babe, he just doesn't love you enough. It's time to move on. I know it sounds ridiculous to end things this way, but I don't see neither of you going to be satisfied any time soon in this relationship.
How bout you guys try not speak to each other for a week or two? See how you both feel after a little break. See if you both miss each other that much/equally. See if he does love you.