Could it be an outdoor plant, looks somewhat like Dipladenia,

A tender perennial or climbing shrub rather,

If so, it loves sun and heat,

And it would need some sort of trellies.

Aeschynanthus, maybe, or Hoya. Can't tell how big the leaves are from this pic.

Yeah, I'd say a Dipladenia would probably look like that after a winter indoors. Not really a houseplant.

Where did you get it from, did it ever flower?

I think its leaves are not thick/ fleshy enough for Hoya, the woody base is not typical either, some of the tendril tips look more like Dipladenia.

Around here Dipladenia is sold as a seasonal plant for window boxes.

It looks like a Vinca to me.

The leaves are not the right shape for Vinca and Vinca doesn't form tendril-like ends to the stems, nor a woody central stem. Also, after a winter indoors Vinca would look even worse than this - most probably completely dead.

Looks like Jasmine to me.