Okay, as an initial comment, violence is never okay. And while I would never resort to violence, I can see why April got so upset. April clearly woke up upset, OP tries to calm her down by being sweet and calling her pet names (instead of addressing the actual issue), so she tells him under no uncertain terms to back off. OP follows her and continues to try to talk to her and solve this in the very limited time in which she should be getting to work, which turns into a screaming match where he calls her a "fucking kid." AGAIN, violence is never okay. But personally, I think OP should have backed off and had this conversation with April later when she came home from work and everyone had had a chance to calm down.

Unfortunately though, this argument got pushed to that level. April has shown that she will lash out if pushed hard enough, so OP needs to consider whether this is a relationship he should stay in.

BUT OP-- this girl is 9 years older than you. She's at a completely different place in her life. While you do pay the bills, she pays for rent (which depending on where you live could significantly outpace utilities). You make money, sure, but you aren't salary. Your income is entirely dependent on whether you can show up for work. Were I in your shoes, I would be trying to stick way more in savings. Which is what she may be thinking as well.

It sounds like you two moved in together without really discussing finances, who will be responsible for what, what will be put into savings. The most successful "living together" arrangements I have seen are when the partners treat it like a mini-marriage, and have a lot of logistics conversations before getting involved this way rather than just the "oh we're in love!" Sounds to me like you really didn't do that.

Time to look for a new place, I think. Even if this is repairable, you guys needs some distance to figure out what you really want.