Why is it so hard to leave..?

I (23 female) am married for almost 4 years to my husband (25 male). We have a 1.7 year old son.

He made me feel so unloved this entire marriage and there have been so many issues. I just feel like I spend my days asking him to love me. He says he does but he does not show it and is a mean, aggressive, and defensive person. No amount of soft communication and approaches, “let’s sit down and have a proper conversation” approaches, written letters, long paragraphed speeches have got through to him. He’s just such a jerk. He just stopped loving me once we got married. I resent him deeply, and I was always a confident woman but now I am not..around him, at least. I’m so tired of telling myself every day for years how bad I wanna leave him. He became physically abusive a few years back and about 4 or 5(?) months ago I left him..I mean just booked a ticket right outta state to get away from him. I felt so happy being away, I was euphoric. He came over there after a month and showed me he was better. I came back 2 months after being away from him and things were great for like a month and a half and then it just started spiraling again. Now here I am, telling myself every day how bad I wanna leave. I’m so unhappy and I cry every day because of our relationship. So why, why is it so hard to leave a jerk like that? I know I deserve better, but I just can’t muster up the courage to go. Whyyy?