Hi silenttulip,
This is a good question. I am recently married myself, so I can relate a little to this situation.
I'm going begin positively and assume that the man/fiance/husband is spiritually committed to serving God, but perhaps lacks discipline or organisation in his own personal spiritual life. Perhaps the woman/fiance/wife could encourage the man, helping him set aside time to focus on spiritual disciplines together. Before someone desires to serve, influence or teach others, they must examine themselves. A person's own prayer life, Bible reading and personal relationship with God should be strong (although not necessarily perfect), so that the person can teach others by their example and behaviour, as well as by their words (James 1:22).
An important verse to consider is 1 Peter 3:1-2, "In the same way, you wives, be submissive to your own husbands so that even if any of them are disobedient to the word, they may be won without a word by the behavior of their wives, as they observe your chaste and respectful behavior." I think this verse indicates the importance of a persons example to others, both a spouse to the other spouse, or someone teaching someone else the Bible. If there isn't some desire to improve their spiritual discipline, this may mean the other spouse praying and studying alone at times, if the man/fiance/husband would rather do something else. This means they are not weakened by their spouse not participating, AND they are setting a good example.
Personally, I struggle myself with having good discipline in these areas. It's something I want to improve. Life can be busy, but it should never be too busy to spend time with God and your husband or wife, learning, sharing and appreciating the abundant blessings God gives to all.
I hope this has been of some assistance. God bless you as you strive to please him every moment of every day!
SteveTheTiger