Is this going to end my relationship?

My boyfriend of three years is significantly more attractive than me, so much so that other ladies have hit on him in front of me and assumed I'm his sister or a charity case. He also looks younger than me despite being 2 years my senior. He is thinner, I am larger than him, he wears a size small to my large, do understand though I am a former long-distance runner so, despite my size, I am fit and healthy. However, lately, more and more ladies are coming onto him and he just got his degree and a house and car (aerospace engineer). I am worried he is going to look around and see thinner and cuter girls and evaluate his life decisions. Should I be hitting the gym, or working with a stylist (I have horrendous fashion)?

Is this going to end my relationship?
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