How to choose a thought?


I’m new to Scholars and I’m struggling with understanding something. I know that circumstances are neutral and only our thoughts create our emotions (and actions and results). So we need to think something useful to get the emotion/action/result we want. OK. But how do you choose this new useful thought? Because you can choose any thought really. For example:

C : My boyfriend is not demonstrative of his affection towards me.
T: He must not like me that much.
E: Sad, angry
A: Not being friendly myself towards him.
R: He does not want to show me affection.
(The result proves the thought, bravo me…)

Now, how do I choose between thinking “He does not have to give me affection as I should be able to provide affection for me, without the supply from the outside” and “I need and want affection in my life and that’s my boundary, my choice”?