Care of tibouchina

Prune after flowering

As this is a tender perennial I think you will find it gets frosted and dies right back in winter only to grow back in spring. I'd leave alone though you could prune back when flowering finishes

I wouldn't risk leaving it outside! Is it in a pot or in the ground, have you left it in over winter before. You do need to prune them back as they get very leggy. I'd do this before the frosts set in and then take it indoors.