The short answer is that he'll be fine, from what you say, just so long as he doesn't marry her!
If he marries her and they divorce then the court will take account of a number of factors in deciding on what is paid to whom. The court may take into account not just money he has earned or obtained since the marriage but what he brought into it, his whole financial circumstances, as well as hers.
Furthermore , if he marries that automatically extinguishes any will he has made before (unless he made the will 'in contemplation of the marriage' i.e because of it ).And, if he predeceases her without a valid will she gets an interest under the intestacy rules.If he does make a will after marriage, in the unlikely event of her not being provided for she may make a claim on his estate.