Be+to infinitive or ing

I know this question might have been asked before,but for native Spanish speakers like me, this aspect is a nightmare. In spanish, every single verb exists without any particle to make it complete; they are always just one word. to be more specific, If we were using Spanish grammar applied to English sentences, those English sentences would read like this:

1 I like read fiction books.

2 I want go to college next year.

3 I need eat something.

Did you notice how infinitives Never take any equivalent to an "ing" ending nor a "to" particle to make it complete in Spanish?

It's very clear that those sentences are incorrect in English. They should read instead:

1 I like to read/reading fiction books.

2 I want to go to college next year.

3 I need to eat something.

That said, the infinitives read like this in Spanish: eat,play,come,see,and so on.

And the same applies when we use the main verb at the beginning of the sentence as the "subject" of the sentence,so again, this is how English sentences would look if we applied Spanish grammar with the main verb working as a subject:

1 Eat healthy is good for you.

2 Play tennis is my life.

3 Go to the doctor is something I hate !

We clearly need to add the "ing" ending to the verbs being used as subjects:

1 Eating healthy is good for you.

2 Playing tennis is my life.

3 Going to the doctor is something I hate!

So, according to the above differences between Spanish and English, almost any Spanish speaker will tell you that they have no problem using the verb+ing ending as the subject of a sentence in English, because it's a bit logical,but on the other hand, our nightmare comes when we have to decide whether to use to+bare infinitive verb or a verb ending in ing after the conjugated form of the verb to be "is". So, almost any Spanish speaker would hesitate with the next sentences:

My problem is to be/being so fat?

All I want to do is to love/loving you?

The only thing I need is to be/being more careful.

Is there any "hint" we can find in "semantics", "syntax" or "idiomatic" aspects of the English lenguage to help us work this out?

My observation on the difference between Spanish and English is by no means an attempt to break the rules of this forums.

It is just that I thought it could be easier for native English speakers to help us out on this issue if they understood what our obstacle is.??