We're getting more into the books here for details but there are two more documented mixed muggle and witch relationships: Tom Riddle's parents and Snape's parents. Both of whom had muggle fathers. While the former's father was coerced, it appears Eileen Prince and Tobias Snape married without any magical inducement. They did have issues because he was abusive to her and she was also disowned by her family.
The wizarding community is small and it's probably not easy to meet someone solely in the wizarding world if you didn't go to school with them, are related to them, or work with them. The community as a whole is conservative and isolated by nature. Interaction with muggles is available to them but it seems to be based on how willing wizards/witches are to explore it. I always thought the dating options in the wizarding world were extremely limited and not something I would like to be born into. It's probably comparable to more conservative religious communities around the world.