Pregnant After Vasectomy- advice please

My partner and I have been together for a couple of years and since he has had a vasectomy, we stopped using other forms of BC about a year in. We both wants kids (he got it after his jest marriage produced twins and has been vocal about wanting kids with me and reversal), we're monogamous, both have stable jobs, IF something happened, it would be good! However, He has jokingly said many times, "well, it's a relief knowing if you get knocked up, you were cheating on me!" (Or something to that extent).