I got asked this question a few days ago by one of my fellow writer friends. She is currently going through a really tough season but she also wants to be a better writer. She had stopped writing completely because she was afraid her writings would be full of pain. The last thing she wanted was to sound bitter or evoke pity from her readers. My advice was simple. "Don't worry about any of that, just write," I told her.
All of our days will not be full of sunshine and beautifully bloomed flowers. Some days are guaranteed to be dreadful. Regardless of the day, once you're a writer you're a writer for life. Our writing is not always for the eyes of other people. Sometimes we will need to write just to get those built up feelings out. On the flip side, sometimes the pain that we are trying to hide from the world is the same pain that will bring healing to someone else.
Our seasons give us something to write about and our pain adds fuel to our fire. We write to release and we write to connect. The last thing we should do is worry about who will think we are bitter and angry. Just because someone offers you their gift of pity doesn't mean you have to take it. Whenever you go through a season of pain embrace it. It won't make you a bad person. It'll make you a real person. Accept the pain so that it can help you and, if it's God's will, help someone else. Not accepting your pain or season won't make it go away.
I implore you to allow your heart and soul to grieve on the pages as you write. After you're done you can decide if you want to keep it for your eyes only or share it with the world. Writing is a gift and sometimes you have to gift yourself. You cannot expect to effectively write anything else when you're trying to bury emotions that are meant to get out. You'll be distracted and your readers will notice that you're not all there. So again, yes! Write with your pain!