I would say don't break up with your agent if the only reason is how long things are taking, or that he/she doesn't communicate enough. If there are other major issues, that's a different story.
I've only ever had one agent--mine--but I feel like I've read your story many times, and it makes me wonder if this isn't how most agents are? Again, I can only compare it to my agent. I love her, I know she's enthusiastic about my ms, but she can take ages to get back to me (to the point where I've googled her to make sure she isn't dead), and in general, things aren't moving nearly as fast as I'd like them to. But I think this is the world of publishing. We hear stories of people who sell their ms in a day, but the painful reality for most of us is that this part of the process takes a long-ass time, and many books will never sell. My agent sent my ms to 21 editors in March, and it took until September to hear from some of them. (One of the ones who didn't respond until September wanted it, but couldn't sell her team on it--so taking a long time is not necessarily a no.) I believe in my agent completely; I just think she's outrageously busy, and a lot of times she's just waiting on editors.
Sorry if I'm telling you what you already know, but it took me a while to understand how painfully slow this process is. This reddit thread
https://www.reddit.com/r/PubTips/comments/b43zlv/pubq_publishedagented_authors_how_long_did_it/ is worth reading. It won't make you feel better, but it will let you know you're not alone.
I spoke to an author of many published books and she said (email quote), "It's VERY VERY VERY common for the book that landed an agent to not be the book that sells first. I talk to writers at this level all the time, and it's really hard to push past the discouragement but it's SO IMPORTANT to remember that you got over that first hurdle [getting an agent], which is monumental."
Think of your agent as the industry professional who will help you write your next book, giving you feedback along the way. You have an in--I wouldn't give that up, unless you had multiple agent offers back when you got your agent, and you feel confident you could get another one.
Feel free to dm me if you ever want to commiserate! This process is brutal.