If you cant handle being in a relationship with a pro athelete then do not date one...pretty simple. When the consequences of losing a fight are brain damage/broken limbs of course you will take that shit seriously and absorb yourself in it.
Who the fuck is going to want to come home after training twice a day, dieting, ice baths, all that shit, and talk about some mundane shit with their partner who literally has no idea what its like to work so hard and put your body through so much?
Fighters should date fighters, someone who can relate to their mindset and lifestyle. Boom