Ho boy, does that hit home! I was married to a cis woman for 7 years and my not having a working part turned into a big issue. I lost her, but that was more because she didn't believe I was really a male, so its not quite the same.
I can give you some pointers from a transmale's point of view. Not having working genitalia can be an issue for a transguy. Having to deal with strap ons etc instead of being completely spontaneous just reminds him that he can't give you everything you need in that area.
There are some very realistic phalluses in different sizes as I'm sure you know, and when I was married, we had two different sizes. I let her choose.
Since it is an issue and you have to talk about it, I would suggest that you don't bring it up during or right after you have had sex. That just makes a guy feel like he failed. If you really love him and don't want to end the relationship, make sure that he knows that you love him anyway, and if he satisfies you, let him know that too.
I'm not suggesting that a strap on is an equal replacement for a normal penis, but it isn't for him either. He may be going out of his way to please you at the expense of his own satisfaction, I don't know and that is between the two of you. I'd like to say its not a big issue, but as you know, it is for some. That doesn't make you a horrible person.
If at anytime, you decide that you aren't going to be able to stay in a relationship with him, tell him instead of dragging it out. He is probably wondering. If on the other hand, you are willing to do anything to stay with him, let him know that as well.
I wish you luck with what ever you two decide.
sam1234