I think you are asking for trouble. I don't know anyone in a committed relationship who tried it without destroying the relationship. When it's three people who have no bonds with each other there doesn't seem to be that problem.
You're right, he'd like to have two girls, if you'd let him. I would too, but I don't think my wife would like the idea.
As for you wanting two guys. I did that before I was married. Me and a guy I worked with and a girl we both knew but had no relationship with except for the threesome. For me it felt weird at first having my penis rubbing against his when we both slid inside her vagina. I didn't ask him how it felt for him.8-|
At first we went in and out together but it worked best when I went in as he was pulling back, then he went in as I was pulling back. She had never done that before and she was always up for it when we called her, which we did several more times. One of her fun tricks was to show us how she could stick a coke bottle in her vagina, so having two penises in there probably was not too much for her. She didn't feel loose though, even when we did it single file. She had tiny boobs and long lips and she used to say God took it away from her top to put it down there. She also loved to have one of us work on her boobs while the other played with her long labia and clitoris and of course her vagina. You girls are sooo lucky, your whole body seems to be one big erogenous zone so the more guys you have working on you the better it is ----- for you.
Then one time when we called, she was too busy to see us because a sub had just come in to port. We figured if she was doing the fleet we didn't need to go back.
But it was fun with both of us in the same hole at the same time and she liked it too.
So I hope you get your chance to experience two or more guys who will work you over lovingly, not just slam, bang, boom.