where did my sex life go?

hubby & I have been married about 6 years,  dating 2 years prior. Sex was out of this world!  Fast forward to the past year, maybe longer... If I'm lucky,  it's barely once a month,  and even that,  isn't a full erection,  sometimes he loses it completely. Initially,  I tried to be understanding Ya know, like stuff happens now & then.  But it's everytime now. & I find him masturbating in bed (frequently) when he thinks I'm asleep,  so he does have sex drive apparently.  He has bought me "gifts" (sex toys) I suppose to pacify me,  or make himself feel less guilty for pleasuring himself,  I don't know. The point is this;  should I accept a sexless marriage?  Do you think there is more going on than I know? I've talked to him about it but I feel like I'm embarrassing him,  so I don't push it.  Just would love your opinions/ advise please