How to catch him?

My intuition is wild these past couple of months. I don't want to waste your time with the details, but everything points to him cheating.

My bf, and recently fiancee has always been a cheater in his past relationships. He went to jail 4 years ago and we are together 4 and a half. The jail part is not so much his fault, no matter how much i hate him after this, the system in my country can easily make anyone a felony.

Just before he was convicted and still in custody, his best friend told me to break it off because he never planned to be serious with me, but i didn't listen. I confronted him and he said that's not true, that he's in love and wants a future with me. Fast forward 3 years i was in a dark place, made a fake fb profile and started chatting with him. He never said to the fake one that he has a gf or anything, and the hothead that i am, i confronted him too soon in the game. He said he knew it was me so he was making it interesting for me. He said he wanted to tell the fake one that he has a gf, blah, blah. I was already in too deep, waiting for him for three years, so i forgave him and we moved on.

From April this year, the jail lets him get out on weekends once every two months. One interesting detail, this woman i know, has her daughter and son in the same jail too. So we went on a protest together and had a coffee one day. One day, she said to call me and she never did. The same week her daughter added my bf on fb and i think they exchanged phone numbers too. I'm not sure when, but i think they started seeing each other in the jail, via conjugal visits. I don't go there to see him anymore because he comes home every now and then, so the slot is open for her.

One conversation that pushed me over happened last week. I asked him what he wants to do for new years and he said whatever, you make the arrangements. As a joke I asked him if he wants me to find some weed or something, and he said: no thanks, i get cheathy on drugs. And i know he took some ecstasy when he was out one time, so i wonder what made him say that. Also, the first time he came for a weekend, when we were about to have sex, he asked for a condom. Which was really weird because we talked about having a baby. So i think he must have had sex with a dirty girl, because on top of everything, i have an infection since he came out.

So the only trick i know is to tell the guy someone you know was cheated on and watch his reaction. I used that trick this morning and he said some vague stuff, like that's life, you can't do anything about it and etc. Also, this morning, I allegedly read his horoscope and told him a bunch of stuff to make him think about what he may have done, and he suspiciously "had to go". I told him his horoscope said he may be doing something behind closed doors, that he's taking more than he can chew, stuff like that

I also want to call the jail in a week to schedule a fake conjugal visit and see if i'm out of the system, because only one wife can visit him. But i'm afraid that if he's really cheating he may have found a loophole, because they are both in the same jail. I think they saw each other yesterday, because he usually works out from 2 to 3 or 4pm, and he disappeared before 1pm yesterday, which is when the conjugal visit starts.

I plan on being very careful this time, because a cheater will try to cover his trails every time, and each time they are more careful. Any tips would be helpful guys, please help me think of a good strategy. I don't know, maybe i'm going crazy...I was cheated on in each of my relationships, so i might be projecting this time