Sal,
In many families money isn't discussed, nor finances, nor budgeting taught to youngsters. Many people I know find it extremely uncomfortable to talk about money for various reasons. A good amount of the time it is because they've never had to or learned to. How many times have any of us talked about money, finances, insurance, investments, etc. with our family members.
He may be embarrased or scared about his past or his current state. It's probably pretty hard to admit that you might be a terrible financial person. I was for a long time. Part of the lying may come from the fact that he's just scared to discuss some things with you. For example [and I'm not saying that your SO does this], he may be afraid of the response he'll get if he calls and informs you that he wants to go out for a drink after work. So instead, he'll call and say he's "working late." The "working late" lie may get a better response from you. Or the infamous "traffic was terrible lie" if he was supposed to leave at a certain time but didn't. Instead of saying "I'm leaving late," "bad traffic" may solicit a better response from you.
IMHO, for two people to be totally honest with each other, they have to feel totally comfortable talking about everything. I don't know anyone like this.
I suppose you can try and talk about finances and the like, and try and convince him that his way is a road to ruin, and your way will lead to financial stability and possibly ER!! I'm sure being able to stop working before 60 is a great incentive. If he doesn't want to or won't talk, you're probably going to be at an impass and you're probably going to have to make it perfectly clear that if he wants to stay your SO [and possibly DH], this is what needs to happen.
My wife and I had a couple of discussions about the division of labor in our marriage [finances, investing, etc.]. It has made our lives soooooo much easier and nicer.
- Alec