Preschool drama

Ugh. My son started preschool 12 months ago at the age of 3 and has been attending the same school ever since. When I ask how his day went, the answer is always that he had a bad day. I've always just assumed he was being dramatic/ thought he was having a great time. And within the last month or two he's started giving more details about his 'bad days' about how he doesn't have anyone to play with. Apparently all the 3 year olds have their regular 'playmate' in the class, and he's the odd man out. He tells me about how different kids tell him they don't want to play with him/ how they don't want to be his friend. We've had some really good discussions about how it's okay if someone doesn't want to be his friend/ that he needs to work on learning how to play by himself sometimes. I thought this was just something that would pass, but I feel like it's just getting worse. It literally breaks my heart to hear about it. Is this normal?!? He is the sweetest little boy. Most kind/ gentle/ softhearted little boy I've ever met. I never in a million years imagined that we'd be having these conversations at the age of 3.