In my opinion, they should've gotten married years ago. Purely for legal reasons. I think it was irresponsible to wait this long. They have children involved both inside (Pearl) and outside (Darcy) of the relationship, they had already (essentially) merged finances by sharing bills, they moved in together, etc.... with no legal protections. That could've gone very wrong for everyone involved if something bad happened.
There's also a huge elephant in the room of how Louise basically had to beg Liam to get engaged. For years. Which is such a red flag, because why did Liam need to think about it for so long? They already had a kid together, which is a much bigger commitment. She even bought herself a ring and got fake-engaged to herself in a video out of desperation. It was kind of sad to watch, actually.
The whole thing just seems like a contradictory awkward mess and I feel like their engagement is somewhat tainted because of it.