What do you think of this "husband"? Actually, he's more like a "roommate."

My husband has a laptop where a password is needed. When I questioned him as to why he has a password, he claims it's because he has too much financial information on it. However, I told him that in such cases you wouldn't need a password for the computer! You would then need passwords for each bank account.

Whenever I approach him while he is on his computer, he turns it off. The computer is located in the corner of his room. He has always been so sneaky and shrewd. I've caught him before looking at pornography in the past so I'm pretty sure he's up to no good again. Even my girlfriends think so.
What do you think? My second child will be going to college soon so I'm wondering if now is the time to make that very important move since I don't want to have "an empty nest." We've tried therapy before and I have separated from him in the past also. He has lied & cheated before. Although we reconciled, it has never been a good marriage. We've stayed together for the kids but soon they'll be all gone & I'm worried. Besides the dog, I have no reason to stay in this household. Figured if he wants to "fool around," he can do it without me living here. Knowing that he will NEVER change, I yearn to be away from him but am scared. Before I do anything drastic, I just want to hear your opinions. Thank you in advance so much for your input!!! I really appreciate it!