Learn Hardcore French: Paul est amoureux de Marie, et Marie est aussi amoureuse de Paul. - Paul is in love with Marie, and Marie is also in love with Paul.

Paul est amoureux
– Paul is masculine → the adjective is masculine: amoureux
Marie est amoureuse
– Marie is feminine → the adjective is feminine: amoureuse

So:

masculine singular: amoureux
feminine singular: amoureuse
masculine plural: amoureux (same spelling, different pronunciation)
feminine plural: amoureuses

The adjective always agrees with the subject, not with the person they are in love with.

Why is it de Marie and de Paul and not something like avec or pour?

The expression in French is être amoureux de quelqu’un, literally to be in love of someone, but in English we say in love with someone.

être amoureux de Marie = to be in love with Marie
être amoureuse de Paul = to be in love with Paul

It’s just a fixed construction:

correct: être amoureux / amoureuse de quelqu’un
incorrect: ❌ être amoureux avec quelqu’un
incorrect: ❌ être amoureux pour quelqu’un

So you must remember: amoureux / amoureuse + de + person.

Is amoureux / amoureuse an adjective or a noun here?

In this sentence, it’s an adjective:

Paul est amoureux de Marie. → amoureux describes Paul.
Marie est amoureuse de Paul. → amoureuse describes Marie.

But amoureux / amoureuse can also be a noun in other contexts:

C’est son amoureux. = He’s her boyfriend / the man she loves.
C’est son amoureuse. = She’s his girlfriend / the woman he loves.

So:

here: adjective (in love)
in other sentences: noun (lover / boyfriend / girlfriend), depending on context.

Can I say Paul aime Marie instead? What’s the difference?

Yes, you can say Paul aime Marie, but the nuance is a bit different.

Paul aime Marie.
→ neutral: Paul loves Marie (could be romantic, family, general love).
Paul est amoureux de Marie.
→ explicitly romantic and in love, usually implying strong, romantic feelings.

Similarly:

Marie aime Paul.
Marie est amoureuse de Paul.

In many contexts they will overlap, but:

If you want to be very clear it’s a romantic relationship, est amoureux / amoureuse de is stronger and more specific than just aime.

Why is aussi in the middle: Marie est aussi amoureuse de Paul?

Aussi means also / too, and its position changes the nuance slightly.

In your sentence:

Marie est aussi amoureuse de Paul.
→ The focus is: Marie also is in love with Paul (in addition to Paul being in love with her).

Other possibilities:

Marie aussi est amoureuse de Paul.
– More emphasis on Marie also (compared to someone else, e.g. not just Sophie, Marie too).
Marie est amoureuse de Paul aussi.
– Spoken French: still usually means Marie is also in love with Paul, but can sound a bit heavier or ambiguous (it could mean: she loves Paul as well as someone else, depending on context and intonation).

The most natural way to mirror the symmetry of the original sentence is exactly what you have: Marie est aussi amoureuse de Paul.

Could I avoid repeating de Paul and just say et Marie aussi?

In casual speech, you might sometimes hear short forms, but grammatically, in careful French, you should repeat the full structure:

Paul est amoureux de Marie, et Marie est aussi amoureuse de Paul.

If you really want to shorten:

Paul est amoureux de Marie, et Marie aussi.

This is understood as Marie est aussi amoureuse de Paul, but:

it’s more informal,
it relies on context,
it’s less clear if you’re not already talking about love.

For learners, it’s safer and more correct to repeat the full phrase:
Marie est aussi amoureuse de Paul.

Shouldn’t amoureux change to match Marie in de Marie?

No. Adjectives in French agree with the noun they describe (the subject), not with objects or complements.

Paul est amoureux de Marie.
– amoureux agrees with Paul (masculine) → amoureux
– it does not agree with Marie.

Compare:

Marie est amoureuse de Paul.
– Here amoureuse agrees with Marie (feminine), even though Paul is masculine.

So:

ask “Who is in love?” → that’s the noun the adjective agrees with.

How do you pronounce amoureux and amoureuse?

Very roughly in English-like sounds:

amoureux → [a-moo-REU]
- final x is silent
- the last sound -reux is like the French eu sound (similar to the u in English fur, but not exactly).
amoureuse → [a-moo-REUZ]
- final -se is pronounced like z here
- again with the French eu sound.

Phonetic (IPA):

amoureux → /a.mu.ʁø/
amoureuse → /a.mu.ʁøz/

Also note de:

before a consonant: de Marie → /də maʁi/
before a vowel, often reduced in speech: d’Alex → /dalɛks/

Can I use the plural form if both are subjects together, like Paul et Marie sont amoureux?

Yes. When you have a plural subject, the adjective becomes plural and still agrees with that subject.

Paul et Marie sont amoureux.
– mixed gender, plural → masculine plural: amoureux
Les deux femmes sont amoureuses.
– all feminine, plural → feminine plural: amoureuses

For couples, you also often see:

Ils sont amoureux l’un de l’autre.
= They are in love with each other.

So the pattern stays:

singular masculine: amoureux
singular feminine: amoureuse
plural masculine or mixed: amoureux
plural feminine: amoureuses

Could I say Marie est amoureuse de lui instead of de Paul?

Yes, you can replace the name with a stressed pronoun:

Marie est amoureuse de lui. = Marie is in love with him.
Paul est amoureux d’elle. = Paul is in love with her.

However:

When you’re talking about specific people already named, it’s more natural and clearer to keep their names:
- Paul est amoureux de Marie, et Marie est aussi amoureuse de Paul.

You’d typically use lui / elle when:

the person is obvious from context,
or you don’t want to repeat the name,
or you haven’t named them yet.

Is there any difference between Paul est amoureux de Marie and Paul est en amour avec Marie?

Yes, there is a regional difference.

Paul est amoureux de Marie.
→ Standard French, used in France and most of the French-speaking world.
Paul est en amour avec Marie.
→ This sounds very Québécois (Canadian French) and is not standard in France.

If you are learning standard European French, stick to:

être amoureux / amoureuse de quelqu’un

Could I start the second part with Aussi: Aussi, Marie est amoureuse de Paul?

Yes, but the nuance changes a bit, and it sounds a bit more formal or literary.

Paul est amoureux de Marie, et Marie est aussi amoureuse de Paul.
– very natural, neutral, conversational.
Paul est amoureux de Marie. Aussi, Marie est amoureuse de Paul.
– sounds like written style or formal speech; Aussi here is more like Moreover / What’s more rather than just too.

For everyday spoken French, the original structure with aussi in the middle of the clause (Marie est aussi amoureuse de Paul) is the most natural way to express she is also in love with him.