Am I heading for divorce?

My husband and I have been married for almost 8 years. We fight constantly and mostly over my kids (none are his, all three were from my first marrige). He doesn't want to work and I have to badger him to get out of the bed. We haven't had in almost a month, and only about ten times in the last year. We work for the same company, I don't know when he would have time for an affair, but it is possible. I just feel like our marriage is going nowhere, and the constant bickering and fighting is destroying my nerves! I can only imagine the damage it is doing to my kids. Should I leave? Is he probably cheating? He is 29, I'm 33. Is the age difference the problem, did I rob the cradle and he hasn't had time to sow his wild oats? I am at wits end, I'm tired of crying all the time. I am tired of feeling unattractive and that he obviously doesn't want me.