Get a new therapist and tell them what happened with the last one, that you’d lie. If you’re open about that, you can tell your story and if it would happen that you’d lie again then you can be more open about it and maybe even talk about why you feel the need to lie.
Try to sit down with yourself and think about what you’re feeling, why you’re feeling that way and what you could do to change it. When you get more clarity, sit down with your boyfriend. Explain what you’re feeling as clear as possible so he can get the chance to understand you.
Don’t flirt with anyone else, probably you’re just searching for something that gives you feelings you don’t have right now. Try to find those feelings within your relationship, and if you both have tried and it don’t work out – break up with each other first so your action don’t hurt anyone else.