Hey, you can retrieve and find deleted texts by getting Dr. Fone. You can get a VAR, voice activated recorder and put it in his car.
But keep in mind in some places a VAR can be considered illegal.
There are also some Key logger programs you can put on his computer to see what he is searching and doing even if its incognito.
These are all considered extreme and many would find this a violation of privacy. But in my mind cheating is a violation of a relationship. it is a violation of life, so privacy is much lower on the list. Cheating can turn into a life or death situation. (Fatal Attraction) so it is REASONABLE in my mind to stoop, yes STOOP to spying. But mostly i think if you feel the need to spy the relationship probably is not even worth the effort. I am sorry your husband has cheated, and IS cheating on you.
Only way for you to actually forgive is to know the extent of the cheating, (You can't forgive what you don't know) and he is not likely to EVER tell you the truth. So you have to chose to dig for it, PI, threaten a polygraph, Dr. Fone, key logger, Expend that horrible energy or just toss the cheating jerk. Honestly....Spying is maddening.... It never feels good. But if you feel you need and still WANT your marriage... You probably need to sleuth.