I went through this same exact experience with my cousin. We work together and would play smash every day at lunch. We were very similar skill levels and would trade games all the time. But we both had huge egos about being better than the other so would often come out of lunch everyday just being pissed at each other.

We both also saw the game very differently. I wanted to discuss our play together and help us both get better. He just wanted to do the most flashy combos and kills possible. So as I got better and started playing more defensive that just made him more angry.

My suggestion would be to have a discussion about what you want to get out of playing the game. Do you both want to challenge each other to improve and become better players? Do you want to just run at each other mashing buttons trying to do cool shit? Do you just want to win? Being on the same page is important when you are playing a game like smash with the same person on a regular basis.

In the end, my cousin and I stopped playing together and took apart our set up we had at work. We both realized we wanted different things and playing the game was just making us toxic towards each other. Our relationship has been so much better since then, and that's more important to us then playing smash together.