Jennifer Aniston Beverly Hills gym Smart Water

We just spotted Jen hitting the gym, Smart Water in hand ... is she keeping her body healthy for a baby, perhaps???

Jennifer Aniston and her biker boyfriend Justin Theroux have no plans on separating, despite online reports suggesting the two stars are on the rocks.

An X17 photographer confirms the pair is still together, telling us he spotted Justin at Jen's house just two days ago:

    "Justin's still at Jen's house -- they've been living together the whole time. They just want to keep their relationship private, but they're 100% still together."

As for the reports the two are splitting, a source tells Now magazine that Theroux is "feeling suffocated" by Aniston.

The source goes on to say:

    "He's crowded out by Jen and her life in LA. He misses his buddies and the intellectual scene in New York. Justin loves her, but she's making him crazy because she won't leave his side. They rarely spend a night apart."

Headed for a breakup or on track for a baby ... what do YOU think?