I don´t know if I´m going to be of any help but:
1st: the sexual/playful aspect of tickling. To understand it try to think for instance of why some perssons are more phisical than others. You surely know someone who is allways giving hugs to everyone or some promoting some other kinds of phisical contact. And that does not authomatically means that persson is trying to flirt or get sexually involved with every single persson he/she hugs. Basically, if you don´t trust your boyfriend near another girl, then you have a bigger problem on your hands which wont probably end or start with tickling.
2nd: The strength of the fetish. As many already said, it´s really different depending on each one. For me it is really big and my sexual life would never be complete without tickling. My girlfriends either understand this and are ok with it or sooner or latter they´ll get too scared that I´ll be looking for it elsewhere. And here you will have a big problem because you know you´re not giving him what he wants and therefore you will see danger on every ocasion he tickles any girl because you really know he is "in need". It´s not necessary to discuss the trouble with little fights that can and will arise every now and then because you are afraid.
3rd: If you want to go for it how can you do it. This will also depend on your sensibility and mostly personality. To this day I had no problem converting every girlfriend into a tickle fan. Usually I go for a softer aproach, I try to go with slight teasing tickles at 1st, we tend to establish some kind of training programe were i will tickle her gently every day for just a few seconds with her in total control and calling the break after 1,2,3,10 seconds, whatever she feels like. I find that if this is made in a very soft and teasing way, together with some massage and a lot of kisses and whatever makes you feel well after it that you will tend to see it better as each day passes. The seconds you are able to stand being tickled start increasing slightly with time. The thing with this is that if you want to do it you simply need to be able to let go. The thing with tickling is not that it makes you laugh, you laugh more and harder from jokes probably. Regular people are not tickled to laugh as hard as they laugh every day with jokes. The problem with tickling is that someone is forcing you to laugh and the catch here is that to withstand it you must be able to give control of yourself on the ends of someone you trust. So if you really love him and trust him, let go of your fears, let go of your restraints, let yourself loose control and remember that you´ll just laugh for a while like you laugh when something really funny happens.
Hope this helps!
But in the end, remember! If you don´t want to go for it, you don´t need to. Maybe you haven´t found yet the right persson, maybe you are not ready yet to submit into being tickled. There are never correct answers in life, each choice you take simply places you on a different path and that´s it!