Help safe my Marriage

How do you safe a marriage, my husband an I have been married for a year an half been together for 5 years , we've been through heart breaks an been hell an back literally. I met my husband while I was 2 months pregnant with my oldest , an then we had our own he was diagnosed with a heart condition an lived for 10 months an passed away one morning. My husband is an alcoholic 24/7 has a drink in his hand .. uve made threats leaving an I have once or twice an came back . He's father an brother are the same so it isnt easy having him work with his brother an dad an drinking all day. I try to bring up how it ruins us our marriage .. I really am stuck an now I'm 4 wks pregnant with our 3rd an now I'm terrified to keep going knowing our baby could have the same thing as our son had or worse be left again like I was our 2nd . I love him dearly he is a wonderful man when he is sober an he is a wonderful father to our son . But I'm still wondering if that's enough... I'm seriously stuck do I keep wondering where life would take us or leave an not return .??