If he is sending texts to his ex about missing him, then he really isn't into your relationship like he may pretend to be. Especially if he is getting texts of nude pics and sex. I know it will be hard since it has been 3 years, but you may want to consider cutting ties.

While I do not agree with everything you did (the lies you told), you were checking up on him for a reason. Something in your gut was probably telling you that you needed to....and sure enough you found things that weren't right. It is hard to trust a person 100% and your gut will tell you when you shouldn't. That is my belief anyway.

Oh and welcome! Let us know how things are going in the relationship and what you decide to do. Would love to hear from you again