I've come to realise that it's often impossible to know, with any degree of certainty, how another person is feeling based on how they are acting. I don't necessarily think that he doesn't care for you. People (unless one is a psychopath) get attached to the people they spend time with whether they want to or not. The difference, I think, is the style of attachment. Some people find saying goodbye easier than others. I think that your T is acting cold and distant to protect himself. Like in a breakup, the partner who has decided to walk away usually switches off their emotions to be able to do so more easily. It doesn't necessarily mean that said partner never cared or "faked it".

I don't think the nice moments you have shared with your T have been a lie. I do, however, think that he is thinking of himself and switching off emotionally to not make this any harder on himself than it needs to be (a selfish, but nonetheless human reaction). The fact that he is getting defensive, such as when he laughed and said your relationship isn't a friendship, points, in my opinion to a degree of guilt. Some people deal with guilt by blaming themselves. Others deal with guilt by turning on the other person because sometimes it's easier to blame someone other than yourself.

I really don't think this is as straightforward as him "faking it" or "acting" for twenty months. Human interaction is hardly ever that transparent. I think you are brave for wanting to ask him this (and you should be able to!), but given how defensive he has been acting, I doubt he'll revert back to being compassionate and caring. Of course, this is purely speculation and I may be wrong, but I really do think he detaching in order to save his conscience.