'to deal with things' mean to handle matters or certain situations ,which are often of a difficult nature. The sentence could also indicate an inability to cope with certain situations or adapt oneself to certain circumstances. " I feel unable to deal with things " could be used in various contexts . Again Liza, the context will help convey the precise meaning here.

"I feel unable to deal with things".= I feel that I can't cope/handle with things[ life, work, relationships] People who say "I feel unable to deal with things". are usually stressed or even depressed.

Here it means you can't cope with life.

In general 'make things right.'