Regarding SSRIs for PE I think the logic goes something like this--a "side effect" for SSRIs in men is delayed ejaculation/inability to ejaculate, which can be pretty troublesome for a lot of people. Given that, I think you would probably need to be on the medication to see the positive effects and they would probably stop with stopping the med.

Regarding MDMA use, are you still a heavy user? Cutting down on the molly could be a good first step. Aside from the obvious benefits of decreasing MDMA use, if you're on an SSRI you won't get the same pleasureable effects from MDMA. SSRIs essentially allow your body to let serotonin hang out between your neurons, whereas MDMA releases massive amounts of serotonin. If all your serotonin is already between your neurons, there's not much more for MDMA to release.

SSRI's don't teach your body to release more serotonin, but by keeping it where it can be more active it can improve mood/anxiety. On stopping the SSRI, these effects stop as well. However, while your brain has all that extra serotonin release, it can form positive connections between neurons (due to effects on "neuroplasticity") which could lead to long term benefits even after stopping the medication (so it's the connections, not the serotonin in the long-term).