I think you should get some time together and communicate about this. Inform him about your desires and confirm on what makes him uncomfortable. You can also consider visiting a counselor for more assistance on this.
Sex is not marriage but it makes marriage better. Don't get married with feelings of agony over the stability of your sex life. It will make tension. Have him checked for hormone levels counseling, emotional issues, talk to him openly and ask him why he's not interested in sex as often as his age predicts he should be? Do you suspect he may be cheating or gay? There are many reasons a man would not be interested in sex. Have you had a child recently? Sometimes interest wanes for men as well, right after having he and partner have a child. How long has this been going on, was it always like this or is this a recent behavior change?