Should I give it another try?

i have been with the father of my children for over 10yrs. We have had our ups, and downs, which has sent me into spirals over accepting his marriage proposals. The thing is I love this man, and I would want nothing more tahn to be his wife, but my instincts will not let me say I DO. He has constantly shown me how immature, and irresponsible he can be, and Iam at the point taht I cannot take it anymore. My children love this man to death, but it is now at the point that they are seeing what I am seeing. I do believe that he has started using drugs, he quit his job, and when he goes out he does not return for hours, on some occassions days. I really dont need anyone to tell me what to do, be cause I have all of my sense. My instincts are telling me that it is not another women due to more detail things that have been done. Some people don't seem to understand how hard it is to break away from someone taht you have been with for so long. I want my family to be together. he thinks that I am over reacting to thesituation, that idea alone shows his lack of respect for me. i guess I just wanted to hear what others had to say about this matter. Your comments are welcome.