As @LaStrega said, obsession spells can become somewhat dangerous, but not just for the target. I haven’t encountered this personally, but I’ve read enough stories on here, from both ends of the equation, to know that you should be careful with this sort of effect. I commented on a thread a while back (link here) by someone who had been targeted by one, which you may want to at least skim over.
Because they are an ex-partner of yours, a better approach could be to encourage reconciliation, followed by lust or love, or both, depending on what you’re going for. If you don’t specify how you would like them to feel as the end result, and only say that you want them to be obsessed with you, the easiest pathway to that state of obsession for the magick to take could be to make them consumed with hatred, or some other undesired outcome.
Not to frighten you, as this should not happen if your desire is clear, but it doesn’t hurt to be careful with this sort of magick. If you follow-up the magick that you have already done with one or two more rituals to steer things where you want them to go, that should suffice.
You may also want to give this situation some time to develop. It does not at all surprise me that my most clicked-on link, with around 50 clicks the last time I checked (5x more than my other most popular ones), is to an article on recovering lost love with magick.
I am well aware that this is an incredibly difficult situation to work through, especially with the possibility of magickal reconciliation at hand, but it’s important to remember that break-ups usually happen for good reason. Magick can always bring you an even better relationship in the future if you allow it do so.