You could ask him about it.

If you ask him, i suggest that your overall manner be "I don't understand and it is really bothering me", rather than "Why did you lie to me?"

If you ask, be prepared for him to get defensive. Stay on your message that you are not accusing him, you just don't understand and ot bothers you and you love him and really want to understand. If he does not ever give you a straight answer, if he attacks you and focuses on the fact that you saw his messages--well that would be a huge red flag in my opinion.

I do not blame you for having this on your mind. You are posting approporiately; post as much as you want/need to.