Worried about our sex life

Hi guys. I really need some advice. I don't want to carry on letting this subject get me down. I've only been with my boyfriend 8 months but just 4 months into our relationship the sex started to disappear.

My boyfriend is mentally ill and was put on very strong medication that seems to of affected his sex drive, he now only wants it once a week or twice if I'm lucky. When I first met him he wanted sex ALL the time, morning and night, he told me that when I'm not around he masturbated 4 times a day to his favourite porn sites. This never bothered me before as we had amazing sex but now it really does because that part of his drive doesn't seem to of been affected. He seems to masturbate more than we have sex. Now it's not me and he wants children one day and never wants to lose me and he finds me very attractive because he never stops touching me as kissing me so just to clear that up. But Every time I'm at work and were on opposite shifts he will go on his porn sites and relieve himself, making him not interested in me later on where in the beginning he could have masturbate AND still want me later....and then later again. I know this because I checked his internet history, he has lied about his usage because he said he only uses it once a week now but evidence showed more like 4 times if I'm not around.

I know the medication has affected him and we do still get intimate but it's only once or twice a week (twice very rarely) when we do it's mind blowing and adventurous and he said he finds me incredibly sexy, he said he has never had this problem before and feels less of a man for not being as into sex anymore.
But it seems that porn is the only thing that can still get him going now and it's making me insanely jealous and depressed and I can't go on like this. It's got to a point where I hate working opposite shifts and I never want to leave him alone in the house and that's not healthy! I want a normal, happy relationship and this is the only thing standing in our way. I've had a chat about this with him quite a few times now and we don't seem to be getting any better. I'm sick of getting rejected and I don't know how to change things, he doesn't know I know how much he really masturbates so how can I sort things out?!