Sources with direct knowledge tell us the couple is, indeed, continuing to date and that they're still romantically involved. Obviously, we haven't seen much evidence of them canoodling in public the way we did in July and August ... but we're told they're an item.

It's unclear what the deal was with Irina's PDA post featuring her ex, Bradley Cooper, just a couple weeks ago ... but, clearly, it hasn't scared Tom off -- as he's still seeing her.

Remember, Irina threw everyone for a loop when she threw up a topless shot of herself and shirtless pic of BC as well ... where they certainly seemed to be getting cozy on the beach, which led folks to believe they might be getting back together. They share a kid, after all.

Unless she's in some kind of open relationship -- which isn't what we're hearing on our end -- then you can assume it was just a platonic thing ... and relatively harmless.

TMZ broke the story about Tom and Irina first linking up ... she spent the night at his pad here in L.A. for two days in a row -- and they were seen being affectionate in his car. After that, they were again spotted going in and out of the same London hotel a few weeks later.

There've been reports that Tom wasn't bothered by Irina's spotlighting of her baby daddy -- and there was even a claim they aren't necessarily in a committed relationship either.