There isn’t a rule about how much sex you should have before marriage in order to make a marriage work or to wreck it. I’m sure that if you were to conduct or read a study on this subject, there would be virgins who married and stayed married to death and people who slept with lots of other people prior to marriage who married and stayed married to death. So, it’s not really about the number of people you do or don’t sleep with before marrying that guarantees satisfaction.
The real question is about personal character. If your boyfriend is at peace with his life and his relationship with you, then that will weigh much more heavily on the success of your relationship than the number of people he has or hasn’t slept with. However, if he’s worried about missing out on sexual experiences with other women, and other relationships, then that’s definitely going to be a problem.
One of the keys to success in relationships is have what I like to call “matching luggage” with your partner, or similar emotional baggage. For instance, someone who’s married, had children, then divorced, and is now dating and looking for Mr. Right 2.0, may be more compatible with someone else who’s also divorced and a single parent because the understandings and expectations of what’s to come are often similar. The same is true with singles who have similar education, socio-economic goals or backgrounds, and social experiences.
But the crux of your question really lies within your boyfriend, not you, because even if you both “sincerely want the relationship to work” if he is unsettled, there will be a rocky road.
I hope this helps.