Anyone who avoids their ex to avoid awkwardness is a coward. People have feelings, sometimes you're responsible for that, Deal it with like an Adult. Conversely, if all of your relationships end badly (like beyond the usual hurt feelings of 'Why don't you love me anymore?" and into full-on bitterness and resentment) then you're doing relationships Wrong.
If you like someone enough to be in a relationship, you should like them enough to take responsibility for what you did wrong and apologize, forgive them for what they did wrong (even if you stop giving them the chance to do it again by splitting up), and recognize that sometimes it's just a bad fit and nobody's fault. If every relationship ends with major heartbreak, you are not looking for a relationship, you're looking for someone to fix you and/or fulfill you. And if every partner you leave is resentful and baffled about it, it's not them, it's You.
It's hard to be friends with an ex initially, but they can be incredibly fulfilling friendships to have. They know you really well and have seen you at your best and your worst, meaning they are uniquely qualified to both build you up and call you on your shit. Oh, and yes, sometimes its a way to cool down a relationship so that you can fix it and get back into it. But not usually, and especially not if that's your intent.
Some of my best friends are my exes, even years and years later. But it didn't happen right out the gates. When I tried that I just ended up back in the relationship. I think you need around 3-6 months (sometimes longer depending on how long and serious the relationship was) before you can get back into that level of emotional intimacy without it being really unsettling.
It can be hard to give it that time when you're feeling raw and lonely after a relationship and you know that this incredible person that you probably still love is out there and could make you feel better, even if they don't love you back in the same way. Or when you're worried that they're going to need you to take them back and you're worried that you'll hurt them more by keeping that boundary intact. Time and keeping busy helps with both. Sometimes those feelings never completely leave, and that can be okay, too. You just have to remind yourself you're a grown-up and every relationship you're ever in is one you choose to be in. And that that applies to the ones you're Not in, too.