I need to know if this is happening to anyone else?

When I first start dating someone, I'm amazing. I exercise, I'm doing well at work, my mental health is incredible. Until I fall completely in love. I start getting mentally ill, then the love I feel for the person I'm dating turns into a love-hate relationship until it ends up being just resentment. I stop exercising, I stop taking care of myself (my physical appearance is very important to me). I start starving myself; it's like once I fall in love, I automatically stop functioning.