How do I let someone in close after a long relationship/marriage?

Very slowly. It's important to not overwhelm your nervous system with moving towards intimacy and connection too quickly. Identify and share your specific needs. It's okay to say, I'm learning and change your mind at any point during an interaction. Find ways that feel good to your system, maybe that's hiring someone to help you feel touch and even arousal without expectations. Sensuali is a great place for that. To move even slower, you can find someone online that is willing and able to help you articulate desires and express yourself before moving into physical and emotional closeness again.