I think around 7 is a really good time to talk to him about sexuality, etc. In fact, if a child asks about these things, I think you should always answer in an age appropriate way. But at 7, they have the mental capacity to understand, without a load of hormones surging around inside them.
My sister is bisexual, although when my DC were younger, she had only had relationships with women. So, it was easy for me to discuss homosexuality in relation to her. It really needs to be presented to them as normal and an everyday thing, rather than something special and different. Children see the social norm of heterosexual couples with children all the time. Most of the children at school are likely to come from a situation where they have one male and one female parent. And books and television etc also assume this will be the norm.
So, it is really important to draw attention to other sexualities, in a way that shows that they are just as normal, and ordinary. You don't have to speak about actual sex acts, of course. Your DS will understand about people loving each other in a sexual way, probably (hopefully, at only 7) without being aware of what that might mean in a physical sense (apart from holding hands, kissing, etc.)
So, you can talk about Aaron loving men (his partner?) in the same way that mummy loves daddy. Just be matter of fact about it, when the subject arises.
And you really need to discuss this with your partner. He really needs to consider these issues. He may have gay friends, but he appears to consider them as "other" - lesser, even. Does he have the attitude of "look at how tolerant I am, having gay people as friends"? Because if he just sees them as equal people with a different sexual preference, why would he be concerned that your son might be gay?