Hello, first I would like to say welcome to the board and say that you have came to the right place for answers. There are a lot of great people on here that are more than willing to lend some advice.
Now, I personally would like to know maybe some more information in order to give you advice. Feel free to answer any of these questions or not to if they make you feel uncomfortable. When you have sex with your partner, who you said is post op, do you use your own bodies or do you use any "tools" ? I am FTM who hasn't yet had surgery and sometimes it is hard for me to get off for a variety of reasons, but I must add, it has nothing to do with my girlfriend. She turns me on more than any woman could, and I am very attracted to her. My personal problem is, and this may be one of the reasons your man cannot achieve an orgasm, that sometimes it is hard for me to concentrate or to identify with myself. My woman and I use tools or in better words, an extension of my own body that I was suppose to be born with anyway. She treats me as if I am all natural and does anything I want to and does it all perfect, but I lack feeling and it frustrates me so deeply. I do the best with what I have, but I want it to work like a bio man. I want all the sensations. While I can achieve orgasm, it is often not fulfilling and often times, I think that I can't orgasm but I am lucky enough to be able to push past that. Without knowing the specifics of how your sexual life works together physically, I can't offer any more knowledge. Feel free to share anything else you would like to share and I am sure the other great guys on this board can chime in and offer a great deal of insight also.