If I were you, I'd get rid of Blossom completely. Use edit town and evict her. If you must keep her, she will have normal starting cash so you could place her in her own small home as far as possible away from your couple. If you keep Blossom in town, she is likely to keep visiting and phoning which will make it harder to rebuild the couples relationship
To start repairing the relationship I would make Shamika ask Dejuan to join her doing something passive (hot tub, watch TV etc.) to start, and make sure they eat together. Also, if you don't already have the "attractive" and "eye candy" rewards, can you afford the points to take them? They can really boost relationship building.