Good morning everyone and Happy Sunday.
My opinion — I personally don't have any issues with cohabiting as long as it is done right and the reasons you're cohabiting are well defined. I believe it can be a learning phase where each partner gets to know the other better before actually committing.
On the other hand I don't believe it's a foolproof approach to a long lasting marriage, as marriage is a different ball game and wether you decide to cohabit or not has little to no effect on wether the marriage would last, I've seen people cohabit and go on to live perfect lives and also that doesn't mean one should do it or not do it as marriage itself is like a consensus with each partner having a 50% vote so I'll say it is more like a situation where you guys have to choose each other everyday, and if at any point any of them decide not to, the marriage can immediately come to an abrupt end. And it has been proven that marriages have a 60% chance of failing.
Conclusion — marriages fail, cohabiting can fail as well, I'd rather fail at cohabiting than have a failed marriage. Thank you.

Thank you @van.illa for the tag.