I'd kinda hoped more folks would've responded to this question by now.
kenji, I'm assuming you're a guy. And like all us guys know, we can't just spring things like this on most women. (Ladies of the TMF are excepted for obvious reasons.
😛 )....so my recommendation is to test the waters a bit by moving in incremental steps.
I'm in a similar situation, but not with a true g/f...just someone I go out with from time-to-time. No commitment there, but I enjoy our time together and being able to sneak in occasional tickles on a cute, fun friend is better than nothing (i.e., numerous generic tickle-free "dates")--which is exactly what I'm likely to have for a time if I spring anything on her too suddenly and scare her off.
However, the occasional, playful tickles serve as good "assessment tools" I've found. Over time, I can get to know how much is <i>too</i> much for her. So far, she seems to complain surprisingly little, but there are signs that her limit is fast approaching. I guess that saddens me a little. ...could be "back to the drawing board" for me, so to speak.
If she ever confronts me (as your g/f did) or perhaps even before she ever does that, I'll just tell her--while I'm tickling her--how beautiful her laugh sounds to me and how much I love her smile. Depending on the mood, I might also let her know that it turns me on to see and hear her laugh like that. (NOTE: These are all true statements I've never told her before.) If she's ok with that, that'll probably buy me a few more weeks of playful (light-to-moderate) tickling at least. LOL Another day, while playfully tickling her again, I might "let it slip" that I really like tickling <i>her</i> (specifically); I might even give a few more compliments similar to the aforementioned ones. If all continues to go well, eventually, I'll just be able to say outright that tickling turns me on and she'll probably not see it as such a weird thing or sudden revelation at all.
In fact, she'll probably say something to the effect of: <i>"Duh...no kidding!"</i>
...then I'll summarily tickle torture her without mercy!
😀