It's up to you to decide whether you and this person share the same ethical values that would likely lead to a good marriage.
However... this may be a cause of "if you have to ask the question, you already know the answer." (That is, if it weren't a concern to you, you wouldn't ask; inside, you already know what you should do but may be second-guessing yourself.)
Anyway, here are some things you could consider:
- Why prostitutes instead of a girlfriend? (Unless it he lives somewhere strict where he couldn't have a girlfriend, which is increasingly rare) I am not advocating having a girlfriend. (Please, no angry emails!) However, if someone has a girlfriend, they are at least demonstrating the emotional and personal maturity to invest in a relationship. Paying for company can be a way of avoiding the inconvenience of actually having a relationship. Is there any hint that this person might have difficulty with emotional commitment to a relationship?
- How do you feel about the religious aspect of violating the command of Allah, and do you share the same religious values and worldview presently?
- How do you feel about the objectification of women involved in paying for services?
- Once a person has done something once, they may do it again. How would you feel if he continued this during your marriage?
- If you are coming from a conservative or cautious religious background (for instance, no dating), it might not be a good match. Among other things, there may be resentment that he was indulging while you were trying your best to be chaste. Also, some women might feel insecure about the possibility of being compared to a professional sex worker.
- Has he been tested for STD's?
- And, how important this marriage is to you? Do you feel like this man is your soulmate and you will be losing out on a big opportunity in life if you pass up on this marriage? Or is it just that you're ready to get married and he happens to be around?
(While some of the above is inherently critical, I do think it is good he is being honest about it rather than hiding things)
These are just some thoughts, but in the end it is your decision, I hope and pray that what happens is the best for both of you.