I had a friend who felt the same way you do, whenwillitend, and I'd tell her exactly what kitty and your therapist have advised, to catch a little time for herself here and there away from her kid, for her own benefit. She routinely refused, saying the guilt that came with taking even an hour or two for herself made it impossible for her to enjoy that limited time in the rare instances she took advantage of it. She even balked at the idea of leaving her kid with her parents, who lived five minutes away in the same town, and who were deeply involved with their grandkid. Though she's a sweet, well-meaning person, and her kid is very bright and empathetic, she created more tension in their household than probably would have existed otherwise by not taking breaks once in a while.

You don't sound like a horrible parent at all; you need time to replenish your energy and take care of yourself so you can maintain the resources required to continue effective parenting and dealing with everything else I'm sure you have going in your life. Find a way towards relaxation by trying it in smaller doses until you feel more at ease with it--you already watch some TV while the little one naps, and there's nothing wrong with that if it helps you unwind. Allow yourself a moment to observe what's happening outside in your yard/garden, indulge in a treat you like and truly savor it, and when the kids are with a sitter or at school, read or catch a movie, even if you watch that movie in increments, or read that book a page or two at a time until you become more comfortable.

All the best to you.