Being positive in this manner is pretty much the basics of Buddhism. I think this will be great for you.
I think you're going to enjoy life a lot more and in general be less annoyed by inconsequential things. It'll be tiring at times, when shit comes your way and you just don't feel like being positive, you'll think "why bother", but do it anyway. This is how you build habits and character. Pushing through the bad because you believe in the good. Life is all about perspective. At the end of the day, it is what it is and you can choose to see the good if you're willing to put in the effort. When you put positivity out into the world, you feel better about yourself. Sometimes a lot more good comes back, but if you do it for that reason you will be unhappy. Be positive because it makes you feel pride.
When people are cynical, negative, passive-aggressive, sarcastic, emotionally unstable, or straight up rude, they are not a joy to interact with. They put no energy into being positive and kind, and in return they have a worse of experience in life. They see the world through a negatively tinted lens and get stuck in a vicious cycle. Putting in the energy to be positive is how you get that energy back from others. "You're a pleasure to be around" is said to those who are kind, funny, open, polite and in general positive. People who have something negative to say about everything are not a pleasure to be around.
Also, it's possible you are an Extrovert and your friend is an Introvert. Some people are energy vampires and some people get tired around others. It doesn't mean anything with regard to positive or negative.
TL;DR: I think this will be great for you. My favorite way to sum up the idea of perspective shaping experience; two people are given the same cake. The negative person says "I don't like vanilla icing, I am not eating the cake" and they are left with a not great experience. The positive person says "I don't like vanilla icing, so I'll take it off and try the cake" and it turns out to be the best damn sponge they've ever had.