How can I be sure if my ex-boyfriend still has romantic feelings for me when we spend time alone as friends and we're both notorious for hiding our feelings?

* You answered your own question by saying 'we're both notorious for hiding our feelings,' and that's probably why you split up in the first place. Communication is even more important than sex because by communicating and expressing one's feelings it humanizes them. There is the possibility your ex boyfriend is not in love with you and someone has to start to communicate so it might as well be you. Pick a time when you are alone and just be honest with your ex boyfriend and if he can't say one way or the other if he loves you then you have two options A) Stay friends or, B) move on from this relationship and get back into the dating circuit.