My husband cheated...

So I recently found out my husband was cheating. The way I found out was that when I got our phone bills it gives us a usage page. Tells you exactly what calls were made, the time duration, what numbers he texted to & what numbers he received them from. So I notice there was a call that lasted over 30 minutes, & saw calls made to this number on other occasions, as well as texts going out to this number so I decided to call the number while my husband was at work, & a girl answered. I asked how she knew my husband & at first she said she didn't know him so I said "really, I saw many calls & texts from this number so you definitely know him." & all she said was "well I don't want any problems, ask him yourself." So I text my husband who's number was it & he freaked saying that I always check his phone, that where did I get that number from so I told him. I told him to stop it with the games & just tell the truth since he had already gotten caught. Long story short, he's been talking to this girl for a year, & had sex with her for 6 months out of that year. The worst part is it's a co worker of his & now she's saying she's pregnant. Should I leave? I'm so confused & hurt. I've been with him for 4 years but it was a year of him living a double life 😔 no one from my family knows & I'm scared to be a disappointment to them if I get a divorce.