There are many variations to this fetish.  Only your man knows what specifically about crying turns him on.  He'd be the best person to ask if you really want to understand.  If you're too shy about asking him in person, maybe email is an option?  If do, I'd suggest bringing a casual, open-minded curiosity to the conversation.  If you ask in a bothered or fearful sort of way, it probably wouldn't go so well.

Having been around the crying fetish community for a while, I've noticed a number of people find the loss of control or vulnerability aspect of crying sexy.  From there, it seems to divide into different sub-interests.  Some people's interests are visual, auditory and/or sensory in nature (tears, lips, sobs, etc.), while others find the psychological aspects of crying appealing, but the reasons can be different.  For example, while many people have a desire to comfort a crying partner, there are others who have a desire to dominate them in a sadistic way, with their consent, of course (this would fall under the category of BDSM practices, which this forum is not really about)).

I find both the physical AND psychological aspects of crying sexy and I think a lot of people here probably feel the same, but my tastes could be different from someone else's within these realms.  For example, you mentioned not knowing whether his turn-on is the combination of orgasms and crying, or just the crying.  For me, I definitely don't need to be having sex with a partner to be turned on by crying because the crying itself is the core fetish.  There are definitely contexts outside the bedroom where I would still find crying appealing.  Like a friend confiding in me about his problems or something like that.  I don't know how others feel about it, though!  It would be good to hear from some men about what turns them on.  But I think, like me, a lot of women don't need it to be directly connected with a partner's orgasm in order to enjoy it.  In fact, some say they aren't even physically turned on by this fetish and explain it as being more of a mental turn-on.

Hope that helps.

Hi Lalaland,
 ​Do you find your man gets turned on when you cry generally? Not just the obvious 'hardness' !! but does he hold you, kiss you, want to watch your tears, kiss/wipe your tears? I would suspect if he has a crying fetish he will exhibit some of these mannerisms. I have been lucky enough to have been having sex with my wife when while she cried and it is a huge, massive turn on not just because I could see my wife crying while we were being so intimate but knowing that she felt so connected, so in tune with me, so comfortable and vulnerable that the surge of emotions and feelings that go through her body during orgasm caused her to cry. If you man is the same as me you will also have noticed his orgasm in a big way right after you! I would not worry about it and if you feel like crying during an orgasm in the future I'd just let yourself go and cry. It will probably enhance your sex life! You did not say how you felt crying at this time?  

Even if the crying isn't the result of sadness.  I'm just saying what the appeal of crying could be.