dear cher,
since you love him so much and plan to live your life with him, it is then essential that you fully and realistically understand that addiction will be a major theme for the rest of your life, and his, and your children's lives. the theme could be wonderful--"recovery"--and all that involves: meetings for him, meetings for you, ongoing, likely for your lifetime. or the theme can be tragic--"crisis"--week after week and month after month. addiction guts a family, and if he is not in active and rigorous recovery, your family will be tyrannized by him and emotionally devastated and perhaps physically abused. this means your children, too.
your higher power is giving you a chance here, cher, to have some say in the future of your family. there will be others along here who will tell you more about what you are facing. but my deepest wish for you, if you love this man, is that you DO WHAT IT TAKES to get some serious help for yourself...through intensive education about addiction, al-anon meetings, counseling....if you intend to go forward and marry him. you will be in this with him, it will affect every aspect of your life, and you need to be prepared.
i'm really glad you are reaching out already. that's excellent. and his avoidance is CLASSIC addict behavior. you are going to need a lot of support in the coming months. a lot is going to go down. so do please prepare.
all the very best wishes for you and your children.