La soledad del domingo por la tarde se me hace más ligera cuando mi madre me llama.

Here se me hace means something like feels to me, becomes for me, or seems to me.

So:

• La soledad ... se me hace más ligera = The loneliness ... feels lighter to me / becomes easier to bear for me

This is a very common Spanish structure:

• Algo se me hace + adjective
  = Something feels/seems ... to me

Examples:

• El día se me hace largo. = The day feels long to me.
• La espera se me hizo corta. = The wait felt short to me.

In your sentence, the idea is not that the loneliness literally changes weight, but that it becomes emotionally easier to carry.

They do different jobs.

• me = to me / for me
• se hace is part of the expression hacerse in this kind of meaning

So se me hace is not the same as just me hace.

Compare:

• Se me hace difícil = It feels difficult to me
• Me hace difícil would not work here

You can think of se as belonging to the verb phrase hacerse in this idiomatic construction, while me tells you who experiences that feeling.

Very often Spanish uses this pattern to express a personal impression:

• Se me hace raro
• Se me hace tarde
• Se me hace imposible

The subject is the whole noun phrase:

La soledad del domingo por la tarde

That entire idea is what se me hace más ligera.

So the structure is:

• La soledad del domingo por la tarde = subject
• se me hace más ligera = what happens to that subject
• cuando mi madre me llama = the time/condition in which it happens

Because the subject is singular (la soledad), the verb is singular:

• se me hace
• not se me hacen

Because ligera agrees with soledad, which is a feminine singular noun.

• la soledad → feminine singular
• therefore ligera → feminine singular

If the noun were masculine, you would use ligero:

• El trabajo se me hace más ligero.

If it were plural:

• Las horas se me hacen más ligeras.

So this is basic adjective agreement in Spanish.

Del is the contraction of:

• de + el = del

So:

• la soledad del domingo = the loneliness of Sunday

Spanish normally contracts de el to del unless el is part of a proper name.

Examples:

• el centro del pueblo
• la puerta del coche
• el calor del verano

Here domingo is being treated as the Sunday afternoon / Sunday’s afternoon loneliness, so del is completely natural.

In Spain, por la tarde is the normal way to say in the afternoon.

Common time expressions are:

• por la mañana = in the morning
• por la tarde = in the afternoon
• por la noche = at night / in the evening

So domingo por la tarde means Sunday afternoon.

In some Latin American varieties, you may hear en la tarde, but for Spain Spanish, por la tarde is the most standard and natural choice.

Spanish often uses the definite article more than English does.

Here La soledad refers to the loneliness as a general, identifiable feeling in that situation. Spanish is very comfortable using the article with abstract nouns:

• La vida es corta.
• La música me ayuda.
• La tristeza aparece a veces.

In English, you might sometimes drop the article depending on style, but in Spanish it sounds natural to keep it.

Not really. Although por has many meanings, in this expression you should learn it as a time phrase.

• domingo por la tarde = Sunday afternoon
• more literally: on Sunday in the afternoon

It is a fixed and very common way to talk about parts of the day.

Examples:

• Nos vemos el sábado por la mañana.
• Trabajo el lunes por la tarde.
• Llegó ayer por la noche.

So it is best not to translate por word for word here.

Because it describes something real, habitual, or expected as a fact.

Here the idea is:

• When my mother calls me, the loneliness feels lighter.

This is presented as a real situation, not something hypothetical or uncertain.

So Spanish uses the indicative:

• cuando mi madre me llama

You would use the subjunctive after cuando if you were talking about a future event that has not happened yet:

• Cuando mi madre me llame, estaré mejor.
  = When my mother calls me, I’ll feel better.

So:

• habitual/real → indicative
• future/not yet happened → subjunctive

That me is different from the me in se me hace.

In mi madre me llama:

• mi madre = subject
• llama = calls
• me = direct object = me

So it means:

• my mother calls me

Without me, the meaning would just be my mother calls, which sounds incomplete unless the context already makes it clear whom she is calling.

So the sentence contains two different me pronouns with two different roles:

• se me hace → to me / for me
• mi madre me llama → calls me

Yes. In everyday Spanish, llamar very often means to phone / to call someone.

So:

• Mi madre me llama = My mother calls me

If needed, Spanish can make it more explicit:

• Mi madre me llama por teléfono.
• Mi madre me hace una llamada.

But in normal conversation, just llamar is enough.

Yes, it is natural and expressive.

Spanish often uses physical adjectives metaphorically:

• ligero = light
• pesado = heavy
• duro = hard
• largo = long
• corto = short

So emotional experiences can be described as if they had weight or duration:

• La carga se hace más ligera.
• El día se me hace largo.
• La pena se hace más llevadera.

In your sentence, más ligera suggests that the loneliness becomes easier to bear.

Yes, but the nuance changes a little.

• se me hace más ligera sounds very personal and experiential, almost like it feels lighter to me
• me resulta más ligera is also natural and means something like I find it lighter / it feels lighter
• me parece más ligera can work, but it can sound slightly more like a judgment or perception than an emotional experience

For this sentence, se me hace más ligera is especially good because it captures a subjective feeling very naturally.

Because Spanish has a fixed order for unstressed object pronouns before a conjugated verb.

When both appear, the indirect object pronoun comes after se in this kind of combination:

• se me hace
• se te hace
• se le hace
• se nos hace

You cannot say me se hace.

This is just part of Spanish pronoun order and is something to memorize as a pattern.

Yes, it sounds natural and quite elegant.

Especially Spanish-from-Spain features here include:

• por la tarde as the normal way to say in the afternoon
• the very natural use of llamar for to call
• the idiomatic expression se me hace más ligera

The sentence is slightly literary or reflective in tone, but it is still perfectly natural Spanish.

Yes. A simpler version could be:

• La soledad del domingo por la tarde me pesa menos cuando mi madre me llama.
• Me siento menos solo el domingo por la tarde cuando mi madre me llama.

But each version has a slightly different feel:

• se me hace más ligera = more subtle, emotional, and elegant
• me pesa menos = more direct metaphor of emotional weight
• me siento menos solo = simpler and more straightforward

So the original sentence is natural, but not the only possible way to express the idea.