Just turned my molly over to my LFS last night...
I gave away my beautiful boy yesterday to an LFS down the street and while I do feel sad, it is a huge relief.
This is chicken, he is a dalmation lyretail that I bought back in February along with 3 girls and another boy. I know already my ratio was off but this is not something that I accounted for being new to the hobby at the time. He was my most beautiful fish despite not having as much of the coloration dalmation are known for. I brought him home with my girl who I still have named cow (for obvious reason) and a not so healthy boy I affectionately named droopy. Shortly after bringing them home I realized that the reason droopy looked so unwell was that chicken was constantly harassing him in order to breed with cow. Fast forward two week I buy 3 more girls (all I could afford at the time) and get them setup which, helped for a while. After about 3 months though he became territorial and began beating up on everyone again. He ended up killing all 3 of the other girls as they were juveniles and then droopy last month then it was only them and cow left. She began looking pretty rough about 2 weeks ago and I'd finally had enough.
Last week I moved her to a mesh breeder box because he was so hard to catch after about a week I swapped them out but I knew that was unsustainable long term so after some hard contemplation I finally took him to the lfs last night and released him to them. They were happy to have him and got him into a tank 20+ other Molly's. I walked around, grabbed a couple fish and by the time I left a half hour later he was already adjusting and looking good as ever.
I had a lot of feelings of failure, and felt bad taking him there because I felt like I was abandoning him but ultimately I can tell this is the best solution for him long term. He will get to breed and his aggression will be checked and spread out in a more natural environment.
I say all of this because I know there is someone else out there who might be contemplating the same but, find a good LFS that you trust and rehome your overly aggressive molly if they are in too small a group. Don't be like me and wait till he wipes out his tankmates.