Welcome to PC Welch90.

Before this past year was your sex life good? There could be several reasons why this is happening. For men who lose their job which result in financial troubles - this is often a big blow to their self esteem. Does he seem depressed - depression and anxiety from stress can affect libido. Does he watch porn - sometimes people can become desensitized to a point where they find it difficult to climax, during regular sex with their partner. Masturbation from watching porn ends up replacing sexual intimacy. The last thing I wanted to mention is, relationships can go through stages where sex becomes routine - they're bored a bit.
Have a calm discussion and ask him why he thinks this is happening - you'll know from his answer whether he needs to see a doctor, therapist or a couples counselor. Sex is a vital part of a healthy relationship and you're wise to get this settled before you marry. I hope you find the answer to your problem and get the support you need.