How do you catch a cheater?

My husband and I have been together for 14 years and married for 8 years. Lately I’ve found dick pictures on his phone in the deleted album, that were taken 30 mins after I went to bed while he was in the living room. I found dick pictures before and was suspicious, but never found anything else and when I confronted him he tried to say he was going to send them to me at work, but changed his mind. However, that’s not an excuse this time cuz he took those pictures after I went to bed and never once tried to initiate sex before I went to bed.

Also, I know my husband takes viagra and he knows I know. It’s not a big deal, if someone needs it they need it, whatever. But he usually keeps the bottle in the house and I found it in his car the other day. Bottle said fill date was in sometime in December for 12 pills, but there was only 7 left in the bottle. I’ll be 20 weeks with our second child this week, and it has been a harder pregnancy than my last. Just don’t have much energy and had very bad morning sickness the first trimester that I ended up in the ER once for. At this point I’ve also caught him twice recently lying about where he was.

I just don’t know what to do. Really looking forward to ideas to help me catch him. One of my friends says she would’ve confronted him already, but for my peace of mind and help in making a decision on my future I feel like I need undeniable proof. If I would choose to leave him and get a divorce, I don’t want him to ever be able to twist things to our children and make it out like it was all in my head and he never did anything wrong.