Hmm not sure if there's no way for Neil to find someone (even if its in the ending) but i think it will be someone unrelated to the story.Neil and Bella is not going to happen. DPC had the golden opportunity to start this in EP.11 and didn't. When Neil mentioned doing Yoga, Jill could have invited Neil to do Yoga with them sometime. The invitation was never made.
Neil must have reasons for not wanting to move on, Neil has never shown any interest in finding another woman. DPC doesn't seem to have anything in mind for Neil's love life. If MC was going to have a new stepmother DPC would have given some hints by now.
But i still think Neil and Bella could be an amazing couple, he kinda has the same goofy humour as james and they both share the tragedy of losing the love of their life (maybe) which could make them more understanding about the partner still being "in love" with their dead spouse.
But yeah, very very unlikely