I think it's helpful to have a healthy outlet for it. I have relationships where we can vent and get it out, and it feels better just releasing it. Not every friend and romantic partner is good for this, so you gotta choose the right person. Venting on Hexbear is also free, if you gotta do that, then it's OK.
Some people find journaling helpful. If you can afford it, you can do therapy, it did help me to vent my bs.
I think it's absolutely fine to need to complain about shit that happened to you in the past. It's really hard to let go if you're stuck in the "I'm not allowed to discuss this feeling in my head" process that a lot of people can get trapped in due to their circumstances. Like not everyone has the social or financial resources. Honestly, I didn't until quite recently.
If you want to complain about your ex in this thread, I'm cool with it. I needed to spend 100+ hours complaining about my ex to get over her, and I wouldn't even consider her abusive or anything.