If you want to be based in N. Ireland you can choose from EZY, RYR, Jet2 at BFS, however the waiting lists at those airlines to move to BFS are very long, I've heard 10 years quoted for EZY. If you managed to get into Flybe, you would probably be in post at BHD within 2 years (I was told by HR), Flybe is probably your best hope of living and flying in NI simultaneously. You need to realise that if you get your preferred base of choice you may have to move out of it once you do your command upgrade; you have to start the process of bidding (as a new Capt) for your preferred base all over again. There are other operators in NI such as DHL, Star Air etc, but again it's a small operation.
On the island of Ireland as a whole, you can add Aer Lingus, Cityjet, Ryanair and Stobart Air into the mix which gives you a few more options. It should be noted however that Aer Lingus is notoriously difficult to get into as a cadet or a DEFO so don't hedge too many bets on it!
With a bit of experience behind you, you could maybe apply for a LH airline such as BA, Virgin Atlantic, Norwegian which in theory would allow you more days off than SH; you could then commute between London and BFS on your days off.
Aviation is relatively small industry in the U.K., nevermind NI. I don't want to get you down, but I would not get your hopes up of working as a pilot in NI in the near future. I'm in the same situation as you so have researched my options extensively, though my girl is flexible and is willing/able to relocate with me. I would suggest that you and your partner seriously consider your options.