Patio Nectarine Tree Flowers But Never Fruits

[BUFFS]

As you can see I don't have much room. Might be hard to tell from the picture but quite a few of the braches cross over.

I would start to train those branches, shorten them to encourage side branches and get a good framework in place before allowing fruit to grow, then its just pick the fruit each year, but they need that framework to grow on sorted first....good luck..

[AkionTotocha]

I believe with nectarines the blossoms fall off because of frost, rather than lack of pollination, because of how early they bloom.

Perhaps something to try would be to cover it with a large clear bin bag from when the buds show to the last frost date, taking it off in the day to allow sunlight (but a clear bag will help if you forget) and for the plant to breathe.

If it's a self fertile kind (which I think most are) then I really do think the frost is the culprit. But a bigger pot won't hurt

[lookbettertomorow]

....and further more, those branches look as though they may have been starved of moisture, then re-hydrated, during the growing season, hence the bare branches with sporadic leafs. This is almost rocket science Dr Watson. If in doubt, chuck it out. The gravel :-)
As others say, cut all back by...well I would go two thirds-but not yet, wait till summer. Cut out entirely the weak spindly stuff and anything that's crossing or growing into the centre, too crowded by half :-)