I would say it seriously depends how health the relationship is. If it’s a healthy one, it can positively affect both your physical and mental health and clear your mind and make you feel better. If it’s a toxic relationship however, it can worsen your physical and especially mental well-being and make you feel down, anxious, angry, or irritable a lot more frequently.
I can’t speak much about this toxic for me though because I wouldn’t know
I think that a relationship can (more so a bad one) affect your health, but I’m not so sure it can. Perhaps being in love can affect your mental health in a positive way.