It really does go beyond simple trust issues for Dora. She actively sabotages romantic relationships when she goes looking for the betrayal she thinks is coming. It's markedly unusual that we haven't seen that behavior in her relationship with Tai yet. We saw it with Marten (even after moving in with them, she would still get upset if Faye and Marten spent time together. And the Marten's porn incident, among others.) Talking about her past relationships this was the rule, rather than the exception. And it is something that bothers her as she has expressed in the past. Then there's the difficult, sometimes bordering on toxic relationship with her brother and to a lesser degree her parents. She tends to shift a lot of the blame of her problems on Sven, when they seem more due to her feelings of inadequacy and jealousy next to him. Not that Sven is blameless, but Dora's problems have more do do with her than with him.
Does she need therapy? Could she improve without professional help? It's possible, certainly. But experience has shown that it doesn't help. She would rather avoid the problem than deal with it. Handling it herself or with the help of friends hasn't worked in the past. Going to her therapist didn't really help either. She was bullied into going by Faye. Then she got defensive and resistant when talking with the therapist. Dora knows she has a problem, and on some levels wants to get past them. But until she is willing to accept the help and do the work she needs to do to improve... Nothing is going to change for her. It might even require an incident like with Faye's trip to the hospital for her to realize how bad it is. Getting hurt on the job or something because she's to tired or distracted. Having half the staff walk off because she freaks out on them because of her issues. Something major happening, basically to shock her out of the rut she's worked herself into.