How to stay motivated when exercising?

Anonymous
My roommates and I are training for half marathons, but every time we train, I always feel so unmotivated. At first, when we began running, I always ran ahead of everyone, but one of my roommates always has something to say about what I do, like running fast. I've slowed down/slacked on working out, and now the same roommate teases because I'm "old" (I'm only 25), that I'm slow or stop a lot. I am super annoyed, it's like I can't win, there's either something that I do or don't do and she'll say something. Plus I've had a rocky month and a half of adjusting to a new country and going to school, which has taken some time to get used to. Any advice?
How to stay motivated when exercising?
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