I said ‘no’ but my boyfriend said it was too late to stop because he was so turned on; is it true that men can’t help themselves sometimes?

No. Anyone, no matter their sex or gender, can control their sexual behaviour and has responsibility for their own actions. No-one has to rape someone to fulfil their ‘needs’ or ‘urges’ or because they’re turned on. There are absolutely no excuses for doing anything sexual to someone who doesn’t want it, or who isn’t able to say or decide whether they want it because, for example, they’re very drunk or asleep. This was not your fault and you do not deserve it.