It will be illegal to be sexual - that is have vaginal sex, anal sex, oral sex, or manual sex - in a public place when someone other than a person reasonably believed to be a willing observer could see it. So sex in certain clubs etc may well be confirmed as legal - it'll be a reasonable belief that someone in a such a space is a willing observer.
It will also be illegal to be sexual 'not in a dwelling' and blah blah blah.
So... sex in your garden = illegal if you know or are reckless whether someone other than a willing observer can see you.
But sex in your house, even with the curtains open and lights on = legal. Provided that you don't intend to cause alarm or distress - that'd probably be exposure, clause 70. (There are other laws - outraging public decency sort of stuff - that could apply, but the approach here is that they shouldn't be looking into your house!)
And, most controversial, sex in a closed toliet cubicle = legal.
Should you have to be sure that non-willing observers cannot see into your house etc?
Should sex in toilets be legal?
Oh, one side effect is that this will update statute law to confirm that male-male sex in the presence of other consenting adults is legal.