Yeah I had a similar experience. Took me a couple weeks to get through it. The feelings still crop up once in a while now, 15 years after being married to her, but I don't ever regret marrying her. In her case, it was only 1 guy in a committed relationship and partly it was just facing the reality that at my age, there simply weren't going to be many women of a suitable age without some kind of experience in that department.

You're right to be concerned. The stats say divorce rates go up with the number of partners a person has had. Bedroom satisfaction goes down. General marriage satisfaction goes down. Rates of affairs goes up. I'm not sure how much being a Christian changes any of that. The one case I know of personally, the wife had a pretty promiscous past in high school and did all the born again virgin and coming to Jesus stuff in college. Married a guy, had three kids with him, had a deadbedroom, then an affair, then seemed to have fixed things only to now be in a deadbedroom again for over a year.

So it depends on how many and what the relationships were. A few one-night stands would be more concerning to me than dozens of times with 1 boyfriend she had been with for 3 years.

You'll mostly get people saying we need to forgive and because we have to forgive it shouldn't matter. God usually doesn't erase consequences of earthly sins, just the spiritual ones. If someone shoots my dog, I can forgive the person and that person get get forgiveness from God and get right with Him, but none of that changes that my dog is still dead.