I may be completely reading this wrong and if so, I apologise, just ignore me.
What struck me though reading your post was that you were able to achieve orgasm 'with someone instructing you on how to play with yourself.' Obviously I don't know what else was going on with you and this guy and you said yourself it was some time ago. If you are the kind of person who attaches a lot of squick and/or shame to masturbation, being instructed by a trusted other can 'absolve' you of that shame, because you're doing what you're told. Maybe it's just the trust that's enough but it may also be possible that you are more capable of sexual fulfilment if the other person is in the driving seat. It's possible you could have submissive urges and get more turned on if you're giving up control to someone else.
I've no idea where 'relaxing' in general comes into this but what I would say is, if you've found a context that works - which in your case is receiving instruction - then if we're talking masturbation, there are plenty of safe ways you can explore this via chatrooms etc, to see if you can replicate what worked before. If it's the case that you're maybe still carrying a torch for this ex though, and he's
more important than the context, well that could be a little more tricky to overcome.
I'm a little concerned you're not comfortable enough in your own skin to enjoy relaxed masturbation. It's something all healthy adults should be able to enjoy. Not that I'm making assumption but if you're on anti-depressants, I do know that some of them can affect sex drive or make orgasm harder to achieve. Alone is when you should be most relaxed though, because if you're not comfortable alone in your own skin, it's unlikely anyone else is going to be able to make you so. I don't expect that sounds terribly helpful but if I'm going to be honest with you, I think it's possibly crucial for you.
Um... hope some of that was useful.