The on-and-off-again couple has been at the center of speculation for over a week now -- and that was kicked into high gear on Valentine's Day when LP stepped out with Marcus in Miami with a massive diamond ring on her left ring finger.

Indeed ... it was very suspicious, but despite people thinking they might be engaged -- this after patching things up fairly quickly following a little spat -- sources with direct knowledge tell us it just isn't so. Instead, it's only a red herring ... a ring from Larsa's own jewelry line.

Now, even though it isn't an engagement ring -- that's not to say this bling isn't nice ... 'cause it is. We're told this ring features a 5-carat yellow diamond with other diamonds around it.

Anyway, in terms of where things stand between Larsa and Marcus at this point -- who very much so look back together and happy again ... our sources are saying they're continuing to work through their issues -- but they're definitely still in love and committed to being together.

Remember, they hit the town on V-day ... and certainly telegraphed all was well again.

Yes, it kinda feels like we're all getting kinda jerked around by these two -- but hey, that's love, we suppose. And on the issue of a possible engagement down the road ... Marcus and Larsa have already said they're considering it.