Usually when completely mismatched couples get together, the fake excitement and passion that they feel for one another is fueled by a brain chemical called Dopamine — not to be confused with eternal love.

This chemical helps to remove the hesitancy, uncertainty and doubts that one might feel so that they can quickly get to the matter at hand — hot, passionate, sticky sex in order to populate the earth.

The street drugs cocaine and Ecstasy work in much the same way.

So once that Dopamine stops leaking in their brains, some normalcy is restored and these couples are often left wondering what the heck they saw in each other in the first place.

That’s the dilemma that R&B crooner Usher Raymond and his ex-wife, Tameka Foster, faced before they got divorced. To complicate matters even further: they have two sons together.

Now word is spreading around the industry that Usher and Tameka are no longer on speaking terms with each other. They say that if Usher wants to communicate with Tameka he sends word through a liaison.

I also heard that Usher has much more than joint custody of his kids, and that the children are with him more than they are with Tameka. But, according to gossip website TMZ.com, that information appears to be inaccurate — Usher and Tameka still share joint custody of their boys, but now Tameka wants a judge to strip Usher of his parental rights because he closed her Saks Fifth Avenue card.

From TMZ.com:

According to the docs, Tameka claims Usher has repeatedly FAILED to obtain her permission to travel outside the state with the kids … which he’s legally obligated to do.

But there’s more … a lot more.

Tameka also claims Usher is required and has failed to:
— get her approval before hiring nannies
— give her first shot to watch the kids when he’s away for more than 8 hours
— allow her to take the kids for 2-weeks in the summer of 2011
— let her have custody of the kids during Christmas break 2010

Tameka also claims Usher closed her Saks 5th Avenue credit card — which he specifically said he wouldn’t do — and now she can no longer take advantage of the “special benefits” the card offers.

According to the docs, Usher also promised to pay $5k per month so Tameka could hire her own nanny for the kids — but he hasn’t paid in months, and now owes $34,000 worth of payments.

TMZ also reports that Tameka is filing for an increase in her child support due to the fact that there has been a “substantial change in [Usher’s] income” since they were divorced — and she wants her cut.