I want a second kid, just not right now

My husband wants to start on a second kid ASAP, and I thought I would too right after our first, but now I just want to wait a couple more years. He wants our kids to be close in age and I know there are some benefits to that, but why not wait? My lo is 18 months and I don’t know if I’ll mentally be able to handle a second right now especially since my husband will be going to night classes three times a week for a year in a couple of months. I also want to take the time to build our relationship with our little girl before a new baby arrives. I don’t know, how do you know if you’re ready for a 2nd kid?