Is comma before "and" mandatory or not?

I only put a comma, sometimes, not always, when I feel like the successive clause could stand in its own sentence.

I only like to talk about the weather, and to go onto a monologue about the great person that I am.

but sometimes I also write it like this:

I only like to talk about the weather and go onto a monologue about the great person that I am.

So is it a mandatory thing. I believe there was a similar thread about comma before and, but the answer seemed to mention the Oxford style, which is when we put a comma between various listed elements and not clauses.

Answer

The comma before 'and' is not necessary because the clauses aren't independent. They're both infinitive clauses based on "I like." I think the answer to this question is clearer when you use a simpler example:

I like to eat and [to] drink.

Examples 13 and 14 from this link: https://owl.purdue.edu/owl/general_writing/punctuation/commas/extended_rules_for_commas.html

are helpful. The basic explanation is that between two verbs or verb phrases in a compound predicate, commas are unnecessary, and the same is true between two nouns, noun phrases, or noun clauses in a compound subject or compound object.