Two males can be an issue, neutered or not.
I would step back and keep them separated for at least a week, have on crated while the other is out. Give a lot of individual attention.Teach them sides. If my basenji is a bit snarky with the annoying Samoyed, I tell him "other side" and he moves fast. With me between them I can have them sit/down and give treats. So they start thinking... hmmmm, both near means TREATS! Make sure for now to feed apart. I honestly prefer in a crate so no fighting or stress occurs. Food guarding is a huge reason for dog fights and dogs biting people. My personal philosophy is that dogs should be able to enjoy their food without stress.
Make time to take for walks.. good for you, good for your boyfriend, good for the dogs. With them on the opposite sides of you both, they get to go outside and enjoy the walk, but be separated enough to relax.
IOW, you want to take some time to help them just relax, not really interact much, so that it becomes the norm.
Engage their brains. Go through basic obedience, working especially hard on down stays and leave it. I use "look at me" then "leave it". Look at me breaks focus on what I don't want them fixating on, leave it reminds them they are being asked to ignore. Mary's lessons are easy, and work fantastic. Plus, it's bonding time, it stimulating, gives lots of opportunity for verbal and treat rewards, and helps you get better control.
Just as you would expect a child or even adult to need time to get used to a new environment, so do animals. If you move slowly, not pushing, and avoiding interactions unless the dogs have accepted the new environment, you have a good chance at harmony. Push them, get a fight, and you may never be able to have them safely alone.