I'm planning to stay with my thai girlfriend in Thailand for 5 months in the coming winter. The METV visa seems to be the best option. I will fly to Phuket November 5 with a one-way ticket, but I will spend the New Year days in Singapore, so I will also have a HKT-SIN-HKT return ticket. I will need an Invitation letter from my girlfriend to upload in the visa application, but I'm not sure if it would be acceptable to make the invitation last for the whole period of 150 days or if she should just let the invitation last from my arrival in Nov until departure to Singapore late Dec.