There are several ways you can approach this issue:
1) Take out sometime for yourself where you work on yourself to see if you can return to your previous spiritual state
2) You can work with your fiance and timetable together for both of you to gain knowledge or do something together which helps both of you spiritually. Although it is important to remember not to be forceful or get into arguments
3) See why he does not pray or what encourages him to pray and then work with him on his positives to help him come back to religion.
As for your marriage, it is up to you to see how you want to proceed. There is much reward in helping others and guiding them and progressing together has many benefits but you need to find the guidance for yourself as well.