Welcome to Aeclectic, Moon Shadow, and good luck with your exploration of Tarot!
The Hierophant in a relationship can mean several things. A few suggestions are:
- the next step along (commitment, engagement, marriage, children, separation, divorce)
- a move towards a more traditional relationship
- a reminder of the forces of tradition in your relationship (especially if you'd hoped to escape them! - for example, you want a quiet non-fussy wedding, and your mother organises a huge traditional do).
- being locked in by tradition
- wise advice received in your relationship
- a bridge between the two, if there has been a rift (the Hierophant - Pope - is also a Bridge).
- a more spiritual element being introduced in the relationship
- faith in your relationship;
- trust (I've had it come as both trust and faith in the relationship and in the other quite often)
- learning from each other in the relationship
- one learning more from the other
(to decide which is which of the last two, look at the other cards. It can refer to the kind of love relationship that has a "master-disciple" element to it).
It will depend on the state of the relationship, the type of relationship and the question asked. The meaning will be different if you've just had a big quarrel, and if you have been dating very happily for a while, but want to deepen things.