Hi Pricilla,
Sounds like you could do with talking to a tax advisor! From my limited knowledge, here's what i think.
When you get married are you going to elect to be jointly assessed for tax purposes with your husband? If so, then payments of interest made by you will be deemed to be made by both of you. Therefore, in your circumstances i think you are able to claim the married person amount.
The reason, i think, for this is that the residence you bought is a "qualifying residence" for tax purposes i.e. it is your sole or main residence. The amount of interest you can claim, provided that you are jointly assessed with your husband, is the amount of mortgage interest paid up to the limit of €8,000 @ 20% (or €16,000 @ 20% when the Budget changes kick in).
As this relief is now claimed at source, you should inform the Bank when your marital status changes so that they can arrange for the increased tax relief at source.
Where you do no elect to be jointly assessed with your husband, your husband would have to be paying the interest on the mortgage in his own right to qualify for the mortgage interest relief. It appears that, as he is not paying such interest, he is not entitled to the relief.
As your husband is renting from you, there are a couple of point to watch out for:
Firstly, taking in rent on a first time buy may have some nasty stamp duty clawback implications.
Secondly, your future husband may have been claiming rent relief on the rent paid to you, this has been addressed in the Budget and may not be available from now on where the rent is paid to "connected persons". From what i can gather husband and wife would certainly be connected.
One final point (sorry about the waffle), putting both names on the deeds and only one name on the mortgage seems like a very bad thing to do.
Hope this is of some help