[Nypbscao]

'Tantra' probably came from Hinduism. 'Tantric sex' is something not really connected to Buddhism and might be more connected with Indian yoga. There is some connection with retention of semen in some Tibetan Buddhists texts I think....but it has nothing to do with core Buddhism whatever people you know say about it.
as a monk - the Buddha would hardly be practising it would he - and he certainly didn't teach it. Anything that says otherwise is a later add-on of some kind.

'Tantric' Buddhism was taken to Tibet from India by Padmasambhava in the 9th century AD - a long time after the death of the Buddha.