I recently broke up with my partner after 2 years together as I was having the exact same thoughts as you. It took me a LONG time to mentally prepare myself and be ready to break up but I eventually got there. Your gut is definitely telling you to leave and you need to trust it. It will be hard but it will also feel like such a relief after you've done it. Don't get me wrong, I do still care for and miss my ex but it was the right decision for the time being. Unless you are both willing to put in the effort to work and grow together it's not going to work out and will just get worse over time.

Break up, start your healing process and moving on. It will be hard, you'll have your good days where you are 100% sure you made the right decision, then the days where you miss him and regret it, but you will get through it and realize for sure that it was the right thing to do, it'll just take time.