once you get the visa, you need to spend some time to different part of Thailand and get a feeling, every city is different so you need to find your place you like...start with Bangkok......seems like you never been there so be ready for cultural shock, Thailand is nothing like Pakistan, its extremely polite and easy to live as long as you stay away from trouble....
there is no guarantee when it comes to having a visa, Immigration officer can deny you no matter what you have, the only guarantee you can have is passport.....
please ask the immigration officer next time and they will let you know. this is not just for Thailand, every country has the same unwritten law, after 6 month you become residence not tourist, sometime they enforce sometime they don't, it depend on the mood of the officer, they can even deny the entry completely even if you have valid visa....let's not argue if this is what you believe then good for you.....
I would advise you to make 2 separate tickets so it's easy to cancel compared to one return ticket, I myself use American Airline, you can make an account and use there app to hold the flight for 2-3 days and then just cancel it....i don't buy return ticket, i make 2 separate tickets... also many travel agents do the same without even buying the ticket maybe they charge 5$-10$ or if you know them then no cost, i just never needed them myself...
i always have return ticket right before i take flight to Thailand and as soon i cross the immigration i cancel it not because i stay long which i dont but my plans keep changing because of my line of work so i can't be sure of my return...DTV is still tourist visa and as tourist we should have return ticket, why take stress and worry about someone in a bad mood at the immigration when it cost you nothing....