In my experience - 17 year olds in 2019 have to handle much more mature and complex influences and pressures than we were exposed to 20-30 years ago.
You will be allowing him private space and time to pursue and develop intimacy with his girlfriend. It is impossible for a 17 year old to have this without some degree of consent from an adult. This is essential for their first sexual encounters to be ones of mutual respect, enjoyment and self discovery. You have the chance to give him this gift - along with the conversations that are an essential part of parenting a young man in this day and age - which will safeguard him from harmful allegations and pave the way to a life of sexual fulfilment, pleasure and genuine respect and intimacy.
Or you can leave them to grab moments where they can, rushing, in fear of being disturbed, in cold and discomfort - I know what I would have wanted myself and what I wanted for my sons and daughter.