I'm hoping this is the right thread, it's seemed to give me the best results on my last post so I figured I'd try again.

I need advice -

Whenever I end up "talking" to a girl everything goes fantastic for the first week or two. We hangout, go on adventures, and just have fun in general and then out of no where I start driving myself insane thinking "what if she's not really into me and she's just letting me spend money and time on her?" Or "she's probably talking with other guys right now" They're not necessarily giving me reason to think any of this, but they're also not giving me reason not to. This recently started with the last few girls I talked to and has been happening rather frequently and I don't know how or why it started considering I used to be the most laid back guy ever.

How can I stop thinking like this? It drives me crazy and I'm almost certain it's ruining my chances with girls. I've never been insecure before and I don't know why it started.

TL;DR : I let my insecurities (or trust issues?) get the best of me when talking to a girl, ultimately ruining my chances with them.