I understand that you are writing it over the beat and it fits... But it's still not written in bar structure.

For "tell her that you love her," to fill an entire bar, the instrumental would have to be at a stupid fast BPM.

By figuring out real bar structure, it will only help you in the long run... Same reason why you don't need to be big into music theory to be a producer, but it will most definitely help. I know plenty of rappers who don't write in bars, and are some of the sickest MCs I know... but that's not to say that knowing bar structure wouldn't help them that much more.