Be upfront. This was quite a shock with me. My SO and I met online. We talked online for a few weeks before we met. He didn't tell me about his (moderate to severe) stutter, and on our first date I wasn't sure what was going on. It sounds ignorant, but I had just never encountered a stutter before. I seriously liked him and after a few dates he felt comfortable enough to address it directly with me. Obviously it didn't bother me as we've been together for a few years, but it probably would have been less of a shock had he been more upfront.