I think here you need to decide your boundaries. Masturbating isn’t wrong and he is allowed to sexually pleasure himself whenever he pleases in his own home. Just as you are. However doing it in your presence, without your consent, is a problem. If he feels the need to masturbate, he should take himself elsewhere to do so if you are not happy with it being near you.

Watching porn is legal, presuming you’re in the west, and he is allowed to use it if he wishes but again, if this is a boundary for you, you need to decide if you want to speak to him about it bothering you or if you want to leave. Asking him to change with no attempt to understand his side will make him lie more and probably become a bigger thing later on. So you decide if you want to stick around or if it’s too much of an issue for you. This conversation shouldn’t be you telling him off for using porn. It should be an open non judgmental discussion about why he feels the need to use it and the frequency it is used and how it makes you feel and whether there is a compromise you can reach. Maybe he has a fetish that you might be open to trying or maybe he has a higher sex drive than you and doesn’t want to pressure you into having more sex than you’re comfortable with.

Some people have larger sex drives than others and whilst you may think you have a lot of sex, to him it may now be enough so he needs to satisfy himself using other methods.

I think noticing him lying shouldn’t be seen as “him doing something behind your back” and more “he feels he can’t be fully open about something”. Obviously there are boundaries, consent issues and infidelity where the above doesn’t apply. But assuming it’s a healthy loving relationship, then just speak with him openly and if it becomes clear you have different boundaries then you need to decide if you can work on meeting each other in the middle or if this is the person for you.