Why do I feel like this and is it normal?

Not sure about your current man, but obviously the one before is no good. If he doesn't know about your current relationship and is assuming you will take him back (again) then you're only going to hurt yourself, again. I bet him calling you with all of that BS made your current relationship confusing since you did have feelings for the one before at one point in time. Perhaps you always will since you share a son. Keep in mind not only did he hurt you, but he hurt your sons as well. There's nothing wrong with allowing him to have a relationship with them but as for the family unit, you're putting your whole family at risk. With this new relationship, it sounds like he is interested in having stability and someone who is willing to commit which tells me he will do the same. I'd say the nervousness is because of the confusion the other is causing. Consider your kids and consider the future. Process it well.