Is my SO bored & not attracted to me?

My boyfriend and I hardly ever have sex anymore. He is literally NEVER in the mood, and when I try to have sex with him he just stops me and ask why I always want to be sexual. It's not that I'm some super horny person or something, we just never have sex like we use to. We've been dating for almost two years. I just don't feel like our sex life should have dropped already. I'm just really confused. Please help. 
I guess I should add in that we found out he has herpes and I do not. Right around that time he stopped having sex with me. Yes, he takes his medicine and we always use a condom. I understand the risk. But please give me advise and don't tell me to leave my boyfriend bc he has a STD. Thanks. ❤️❤️❤️

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