You've got a lot of conflicts there, and one way to give yourself some antagonists for your characters to actively work against is to have these conflicts presented by a character. Here are some examples, taking the conflicts you've mentioned here, and imagining a character who could represent them:
Boy's guilt over leaving mother: A doctor who diagnoses her with an illness that requires long-term care at home. A social worker who will visit regularly to check they are okay. Pressure from other family members to do his duty.
The girl's conflicting dreams: A family member who is worried enough to have her see a psychiatrist. Psychiatrist recommends drugs that repress or change the dreams. Or she is watched for signs that she's not in touch with reality, and she is admitted to a psychiatric ward.
Suspicions that boy is a murderer: A police investigation is ongoing, and the boy is a suspect. Evidence is building up against him, and there are detectives watching him, taking him in. Social pressure from friends or neighbours, stirred up by local press.
The ex-boyfriend and the person framing the boy (if they are not the same person) will be acting to pursue their own interests, which should interfere with the plans of the girl and boy constantly.
Do you know why it is so important for the two to meet? What happens if they don't meet? Why do they trust their dreams? You could have another character who suggests to one of them that the dreams are a result of medication, recreational drugs or stage hypnosis, something they once did. Will the boy lose his job, because he's always daydreaming? You could give him a boss who tells him to shape up or he's fired - and that would stop him being able to afford to travel, or support his mother. Have some repercussions looming if they don't meet, so it's not just a case of living with wistful dreams of "the one that got away" type. If there is a specific threat they're acting to avoid by looking for each other, that might also suggest characters who could stand in as antagonists.
It sounds like your ex-boyfriend and framer characters are good candidates for the antagonist. You could build their parts up, perhaps combine them if they're different people, and you could end up with someone complex enough to be the one antagonist.