I don't typically do this here, but I have to offer a contrasting point of view. My wife is not keen on being tickled, and in all honesty isn't even that ticklish. She gets there with some oil in the right spots, but that takes some effort. The point is, though, that I love her and she is my best friend and supports me in ways I didn't know I needed. I know how cliche this sounds, but bear with me. I chose that over constant tickle fun, but it doesn't mean I threw in the towel.
I've convinced her over the years to let me tie her up here and there, and we're hitting our stride in that finally. I can get some tickles in, and that's great, but the real turn on is that she trusts me enough to take those steps.
I know in your heart of hearts you've already made up your mind, and you need to be true to both of you. Love her because you love her, or let her go because you don't. And then don't look back and don't regret anything ever. I know it sounds sappy, but I honestly believe this. Don't break up something over anything less than "not love". Everything else bends to that. The whole tickling thing is just an excuse, not the core question here. I'm not saying to force it, though, either. You either love her or you don't, and if you don't you'll grow to resent her in ways like this, so don't do that, either.
Good luck, dude!
I want to endorse this. If you really have something between you that feels like love, then you might have to decide whether you can take a big breath and sublimate your tickling urge in the service of something that frankly could be deeper and more meaningful in the long run.
When I have thought this problem over in my own life (admittedly not ever being in a position where I have been forced to make the either/or choice for the long term), I have found that for me it is actually more important for the woman I love to BE ticklish than for her to let me tickle her. I love her ticklishness, along with a whole lot of other things about her, and in the end that is enough. But it may be that I haven't got the fetish as badly as some people, so I can sublimate the tickle urge and express it in other sexual and emotional ways more easily. (Not that it's that easy...)