No self respecting man should give a second chance to a cheating whore, the moment that happens, she gets dropped like an old habit.
Exactly.
There's really not much one can do about her infidelity but there are things a man can do to minimize the possibility of it taking place: 1) she must know you are checking up on her, 2) you must check her phone once in a while without her knowledge, 3) no girl's nigh out or vacations with the girls, 4) you must visit her at work at random times, 5) you have to LISTEN to what she says to you about people (women tend to telegraph the fact that another man is in her head,) 6) you must attend work related events with her so that you can gauge any potential shenanigans, 7) any flirting from another man has to be quickly shut down by confronting the man on the side and promising real pain if the flirting continues,

you MUST communicate your boundaries often and what you expect of her as a wife/girlfriend and 9) try to get to know people she works with, preferably those that barely engage with her, and establish a line of communication so that if they were ever to see something weird (like her going for a coffee/lunch break or drinks after work daily ONLY with 24 year old Brad Thundercock from accounting) they would let you know immediately.
If you let your lady roam free, there is a very high probability she is going to cheat on you.
Ah, before I forget,
the mere mention of her ex should elicit a very strong response from you. Bringing him up not only means that 1) he is still in her head, 2) he is trying to reconnect and 3) there's a very high probability she is sexually active with him. The % of cheating that takes place with exes is OBSCENE. Women tend to start relationships without properly letting go of their exes and the lingering feelings are seldom properly dealt with. That's why it's also a great idea to DNA the kids for paternity.